I'd be more concerned with making sure the brakes, suspension, and the rollcage going in will do the job for a low 10 / high 9 second car.

As to the engine, there are plenty of ways to go...

A 502 built up for a medium size shot of nitrous.

a 402 built 70's style for maximum performance, which will mean minimal streetability. High compression, square port closed chamber heads, and a big lumpy cam.

A 6/71 blower.

Also, you might consider dropping the TH400 for a powerglide instead... less parasitic power loss.