I was told that you cant use these GM crate motors for re power. I was told that you have to change the cam, valves,springs, and heads. The motor makes its power at 5200 rpms. Has anybody done this.

I am using a the zz502 heads,intake and cam in my 454. I am very happy with it. Do a search on zz502 and you will find enough info to keep you busy for a few days.