I bought a rebuilt 355 SBC complete for $500, i sold it the other day in favor of the LSx motor, the aftermarket is exploding for them, and running EFI has never been easier, if you find a LSx motor out of a vehicle, you can grab that PCM and harness, and hook it up with as little as 5 wires to make it run on the floor! i've looked into these way to much. you would want to get a 00+ motor as they changed the oil galley, and get a washer to put in the oil pump to bump up the oil pressure, as they are known for loosing oil pressure at high RPMS.
If you get a LSx (and there called LSx because the heads and almost all parts are interchangable) a LT1 is a revision of a SBC, and yes, the after market and parts are limited, and the opti spark is a big headache. if you want more wiring info to run EFI with extreme ease, check out these guys.
www.eficonnection.com
i hope this answers your questions, if you need any more info from me, just send me a PM as i'm over flowing with info in my head about this swap.
I'll try to check in again into this topic if i remember.
Bob