If you prefer the FIA, as I do, then stick to the small block as the cars are so light it really will not matter. You could also do as a SAAC member did with a slabside = 427 windsor or even Clevor. With today's technology you can have a 427 SB with reliable and gas efficient operation.
This will be screaming fast!
If you go 427 car, I would suggest a punched 390FE as you will get original look and again with today's heads better than original power at 1/2 the cost. Most of today's replicas are faster than the 60's cars which is possible with 40years of tech.
Best of luck!