Beginner Road Track Racing: Feedback on Engine Options Wanted

Competitive? What if the guy just wants to have fun and loves these cars?
That is how I am. I want to do some stuff like this eventually. I would use an A body though just because while I'd prefer a B body, the replacement cost of a 68-70 B body car is outrageous. A 73-76 A body roller can be found for well under $1000.