Two question. First off, will a Gen V 502 heads bolt-on to a Gen VI 454 MPI?
Second, does it offer any performance benefits? The particular heads in question are Mercruiser "Hi-Perf" heads.

The combustion chambers on the Gen 6 MPI heads are about 98cc. The MAG Rec port heads are 118cc. You would not want to change them. Also intake would not match up.

There are several things to look at/clarify before you do this. 1st are both heads square port? If you are changing to the square port head I don't think you will see any difference because the cam & compression is so conservative on the non-mag motors. The other thing to look at is a gen 5 head will fit a gen 6 block, but I am not sure about the coolant passages lining up correctly. I think they do. If I rember right the gen5 & gen 6 heads are interchangeable between generations, but they will not work on mk4 blocks without coolant passage modifiers.

Thanks very helpful. I was curious more than anything else. Obviously, not very familiar with large blocks.