Bracket engine, what would you build and why?

I would use one of the 400 blocks and put a 440 crank in it to give you 451 cubic inches. This is a very popular build, and makes great power. Very simple, and only requires a little machine work and offset grinding.

Would be less weight on the nose of the car as well, since the deck height of a 440 is about 3/4 of an inch higher than the 400. Lose the weight and keep the displacement.