The crank look to be modified a bit, Not sure if the photo links would work, but here goes:

Notches

Notched

Chamfering

Surface Machined

Are the Piper 255 and SW5 cams similar? I've seen recommendations for both of them 
I have no experience with either 
Thanks!

Yes - it's a great idea.

The 1098 is my engine of choice, even over a 1275.

Go to +.060" on a straight rebore to ensure good bores, 12G295 head or a 202 if you can't find one, balance the crank (important), Piper 255 cam, compression ratio around 9-9.5:1, and it will pull trees over.

Don't rev it enormously (going much over 6000 isn't a great idea), but the wall of torque makes it unnecessary anyway.

I have the core 1098 that I'll be rebuilding 
The crank shaft looks to be modified with some surface material removed and other tell tale signs
It would definitely need to be checked for cracks or other defects. Both main and con rod journals show 0.020 on the bearings as well.
CalverST sells some pistons developed by Russell Engineering for the 1098 - I'm guessing this is the way to go
Along with an SW5 cam and the original A+ 998 gearbox and FD, I should be all set  

It's not rocket science. If you want an 1100 build (I like the 998 for revs and reliability) you need either a 998 or 1100 block (the same) and 1100 crankshaft and pistons (1100 pistons are shorter due to stroke). The 998 and 1100 rods are the same.

PS. The 'Graham' that the previous poster is referring to is Graham Russell. Some call him God, others don't.

Since you are possibly heading down the 1100 path, I'd recommend the Graham from Australia list of mods for the 1100. As seen on Rick's 1100 build, you can get very good performance with the correct parts and machining. I'll try to find you the link, but you should start with ausmini.com, as they are all fully aware of Graham and his company ( and the "Standard" list of mods ). Best of luck in your build! MSH

p.s. if you'd like another head to work with, I have a 12G202 1100 head that might help. let me know

The 998 A+ currently installed is damaged because of a suspected broken ring 
I found a bare 1098 block which looks to be in great shape and another 1098 that is assembled but siezed due to weathering without the head installed.
should  I pursue the idea of using all three engines and building a good running 1098 using parts from all three units?

I’d like some opinions and ideas before making any decisions

thanks