360 vs 383
Senario 3... i'm fine with a 11sec bracket car, so the 360 in a A body or 383 in a B is where i'd go here.
As far as senario 4, all bets are off. Really depends on the class or et needed to compete.
All that said, i think a moderate compression, mildly cammed, low rpm, 470/500'' B engine would be a blast in any A body with low 3gears and give many street miles with fairly low maintenance.
Now, if i was only 20/30yrs younger...:)