[Alan Roehrich]

A 1971 512 block should be a 454 with either 2 or 4 bolt mains, may have a steel 454 crank. There is however a possibility that it was a 427 service replacement engine, but both the 454 and 427 were 4.250" bore. If it truly has a 4.125" (402) bore it is rare indeed, and it is possible, if highly improbable. Good old block, I like finding them.