Isn't that the way it goes, decide to get involved in a build thread and it fades away. OK, back to it. If you have 93 octane for the foreseeable future ( does that look like a word? ) you can plan on running from 9.5 up to 10.2 CR. The idea is to set your block up for zero deck clearance. All pistons coming to the deck flush. This should reduce detonation. You will still need to be very careful with your fueling and dizzy advance curve. I'm not a big fan of the very expensive numbered dizzy. I'd suggest you contact Jeff at Advanced Distributors once you have all your figures on the engine build and have Jeff build you a dizzy.
Someone was talking block prep yesterday. On true race engines I have a steel four bolt center cap installed and line bored as well as ARP hardware. The block is also driled and tapped for the extra head studs. Cyl. boring and honing is done with a deck plate in place. I also have a set of long drills and fixtures that allow me to drill all oil passages out 1/16 larger than stock. Then if the passage does not line up with the hole in the bearing shell I move the hole in block around a little. Run a tap into all threaded holes and install cam bearings properly to control oil flow to the cam.
There is so much happening with cams now it's hard to say what to use. I have always like the ST 643 cam for a street/ autocrosser. With a good intake/exhaust system and 1.3 rockers it should pull well from 1800 though your target 7500. Have Swift / Calver or someone who still ports heads do one to your specs. Calver is less likely to go over board on intake port size.
As for engine size I like to go up .020 at a time. I currently have a 1360 Cooper S that I have worn out at each over size in the years I have run it since 1971.
Now you mention trannys, you can select something from around $1500 to more like $7800. If you are going with SC drops spend the extra and get a taper bearing idler gear. As mentioned before a center oil pickup is a must and a windage tray would be nice if you have an extra $100 more less. Buy the best synchros and shift forks you can find. Careful shifting will help them last, abuse them and they can be done in a day. It would be the same with 4 synchro SC/CR. You have not said what type track time you are looking at. We like to use a 3.9 or a 3.7 for most east coast tracks. For a serious autocrosser 4.10 / 4.26 or 4.35 will serve you better.