I recently ran into almost the same problem. I replaced the exhaust manifold in my car (Mk1 with a 1275 of unknown origin). After a quick drive I realized that it was idling really high. It turns out that the new manifold was limiting the travel of the throttle linkage that connect the dual HS2s. No orientation of the triangular butterfly linkage (12A310) would clear the center pipe of the exhaust manifold. Finally I realized that I had the wrong manifold on the car. It is a 12G299 that appears to come from an MG1100 with the 10 degree angle on the carbs. I’ve borrowed a 12A661 to get the car back on the road, but now I’m trying to decide what to buy as a permanent replacement. I’ve always felt that you never squander the opportunity with a repair to make something better than it was.

 

From reading around the web, it appears like there is little love for the original manifold from a flow / performance perspective. Since my car is already a frankencar, I’m not overly concerned with keeping it all original. What manifolds are people using with their twin HS2s? I’ve seen a number of people recommend the Maniflow option, but details are scant.

 

Any thoughts or suggestions?

Your carbs, manifold and spacers exactly match a set that I just started to refurbish, and mine came from an MG1100.

You can re-use the carbs on a Mini 1275, but you need manifold C-AEG488, half inch longer throttle and choke rods, and a pair of 30° carb float grommets AUC1316 and AUC1136.  The needles may need changing as well, M for standard Cooper S spec. All available from our host.

Certainly starts with a manifold issue. Tabs on both my float bowls equate to single-carb Mini. Looks like you folks have zeroed in on each issue and now I need to decide which direction to go and what parts to collect. No hurry now though. Got all excited with our past several days of sun and 50F, but now back to normal - 30F and 6 inches of snow due in next 36 hours. I had not been actively on this site for several years and I had forgotten how helpful and giving you each can be. Thank you very much all!!

You can tell just by looking at your last pictures John, that the carb/manifold angle is def not mini

This is how they should look (angle etc. )

Looks like you have a 1275 A series. If you google the number on the carb tag as i suggested you will know what you have carb wise and probably intake wise as well.
If you do not have the depressed area below the speedo hole and want to use a single carb you may need an MG Metro intake to clear the bulkhead. It sometimes can be done without that intake but will require a thin spacer and massaging the linkage.
If you don't drive in extremely cold weather and decide to use a HS4 you can cut the intake off a cast iron intake/exhaust combo and that will give you the correct angle and clearance, if not you may need a water heated inlet manifold which most if not all aftermarket ones are.
Unfortunately there is no one answer to the carb interchangeability on Mini's that have had engine and exhaust changes and it may well be cheaper to fix or alter what you currently have installed.

CTR - Not sure who built engine. That quote was from 2 PO's before me and I got the car in 92. It was sold in 89 to a friend of mine (-1 owner from me) and he and I picked it up with his FF trailer with engine and Gold Seal rebuild out of the car. That was the time when the "guy in VA" quote was made. All the receipts that came with the car were from Se7en. -1 owner and I got a kit (I think it came as a kit) to mount this engine and rod change box in place of long-gone magic wand. He gave up on project after a couple years and sold it to me. Don't know if you can tell from pics but there are rivets on the block for # tag, but none is affixed.

+1 to jedduh01's suggestion for a HS6. I have a HIF44, which frustrated me until I replaced the bi-metallic lever inside that makes tuning a chase-your-tail event. A stationary Mini heats the carb causing the bimetal gizmo to lean out the mixture, while you are trying to adjust it. I made a non- bimetal version that works perfectly. The HS6 would do away with the issue entirely. On my car, the HIF44 bowl is about 6mm from the bulkhead cross-member, which in my car has the depressed section found in later cars.

Carbs from whatever seems to be the theme here...
  It looks like if you even just go thinner Carb spacers the Bowls will contact the heat shield... by being pushed in more.

That still leads to needing the correct bowl angle mounts and a manifold with shorter studs (shorten the spacer the studs left will be too long.

I have a HS6 ,  Single Carb SU on my car and love it = Easy access all around.  No Integral lower bowl like the HIF to contact the fire wall= Easily fits.  You can get a HS6 From a Volvo p1800,  little bit of work on the linkages and it will work.

Either way you go youll be replacing the Manifold

https://www.minimania.com/part/AUC1366/Classic-Mini-Su-Hs2-And-Hs4-Float-Bowl-Grommet-30-Degree

There is a good chance our Forum host has used parts to piece together a 'proper' mini intake setup.  Give them a call!

AA s did not come with twins. If more narrow spacing most likely a MG 1100 set up. The K&N filters are off set to clear master. Any idea who in Virginia built it. I have been here all my life and into minis since 68 know most guys who were into them back then. Give us a wider pic. I'd be surprised at a Metro engine getting over here back then ( early 80 s ) is it A+? Steve (CTR)

I believe JEDDUH01 may be right with the Austin America idea. I have seen 2 of those in the past with twin HS2's. I also have a Sprite and the angle between the manifold on that 1275 and the one on the Mini seems the same but the carb mount spacing is different. Sprite carbs mounting is 1/2 inch wider - about 6" vs 5.5". The tab on that left float bowl is stamped AUC 976 (F R or R L). That spacer on the S setup is really thin. Mine started life being the same thickness as the one on the Spridget, but is a full 1/2 thicker that the one above. Changing to that spacer may solve both the clearance and air cleaner situation, but I still would be using incorrect intake. I wish I did have BC's $ so I could start completely new. But...I am married!

I have an Austin America 1275 engine with the MG 1100 twin carb set up (AUD 69 L & R) in a 62 pick up i just bought and they clear fine but it is RHD and will be changed to a correct 30 degree set up.

Austin Americas did not come with twin carbs. That would not be a good bet to make.

While the inlet manifold, spacers and float bowl angles are wrong, the exact style of wrong, be it MG Midget/AH Sprite-my own guess or perhaps twin carb ADO 16 derived is hard to tell. Still, the right parts for this are all that is needed.

The casting number should be in the same place as the pic that jedduh posted or close. If not the triangular tab on the float bowl in your pic should have an AUD ... 2 or 3 digit number and this will tell you what application the carbs were used on. As yours has a pcv set up it would probably be an early set of carbs.
LHD and twin carbs is tricky but can be done with the right parts. I have seen offset pancake filters for sale which work with LHD. 
If you do not have the lowered section under the speedometer hole in the bulkhead a HIF may be an issue to fit without moving the engine forward. If you really want to go with a single set up a HS4 might be your best option.
Another option is an adjustable steady bar but it will not give you all the room you need.
Also another thought is maybe the newer plastic master cylinders have more clearance as their bowls sit more to the rear.

Here's a shot of Spacers + manifold for an original  Cooper S Setup.

1/8th spacers for sure.
The manifold has more angle
and the float bowls have corresponding correcting angle too.  

I would bet your whole 1275 Lump is from an Austin Amercia and the front timing cover stil lhas the 'tabs" for the different frame mounting of the AA =  the swap is done in to a mini but these carbs needed to change to be PROPER.

Replacment Manifold will kick UP the carb angle
  Have shorter studs for the thinner spacers
and thus convert the space behind thecarbs to aid in filters...  Proper filters must be sourced too  LHD are 'different " because of the Cylnders in the space.

I would just buy new carbs from www.burlen.co.uk and be done with it..  BUT  I have to cash to burn later bc

I have an almost new HIF 38 on a mini manifold if thats any good to you $100 plus postage?

HS4 manifold You could try searching this site
spacers

If you buy the right manifold and spacers and floatbowl mounts then you will be fine.

It is that easy.

One other point that is often not mentioned: speedometer cables have a hard time passing modern single carbs with performance oriented air filters.

I pulled off the stacks and took a couple more pics. 1. Lt carb float bowl sitting against the brake master mount. 2. Rt carb float bowl hitting stiffener plate just near where the heater hose passes. 3. Small space where an air cleaner would need to fit. Note from photo 1 that there is very little between air cleaner mounting bolt and bean can brake MS reservoir. I tried pancake filters and could not line up bolt holes for that reason.

Cannot read any casting number on intake while carbs are mounted. The phnolic (sp) spacers are 5/8" Can reduce them more but cutting them and the mounting studs in a PIA.

I have been talking with a guy in Britain with a HIF44 setup using a Metro intake. Have also been looking for a setup using HS4 but have not found one.

I was told this engine was a Metro unit built back in the 80's by "some guy in Virginia"

On the intake manifold you will find a part number or casting number.  You can then Google this number to figure out what the manifold is for, be it Sprite/Midget/Austin America/MG 1100 or even  possibly one for a Classic Mini.  Then you will know whether you have the right manifold.  Should be a 30 degree manifold vs a 20 degree one used on the Midget and others.  You say you have thinned down the spacer block by 1/8".  How thick is it now? The spacers on my Cooper 'S are in the 0.250" inch range ( 1/4" thick ).  The other advice about the 30 degree float bowl grommets to match the 30 degree manifold, the right needles in the carbs and your choice of Mini type air cleaners without the ram pipes and it should work for you.