543 0R 505

If it were me building a bracket motor I'd build the 543 and let the extra torque work for me. Keep the rpm's down and it'll live forever.

A buddy of mine runs a 500" or 505" with a glide in a light tube chassis Dart. He turns it something like 6400 and it runs 5.80's. It goes a loooong time between rebuilds. The lifters get changed every couple years and the springs checked but that's about it.