A friend of mine has a 1998 checkmate with the 7.4 mpi motors 310 hp. His heads are junk. I can get some 1993 454 330 hp heads that are pretty much brand new. Will these older heads work on the newer blocks? I didnt know if the rocker arms etc, was the same or different. Any help on this topic would be a great help, Thanks

The 1998 heads should be Gen IV large oval L-29 heads with small chambers. These heads are better than the small ovals from the 330. I have heard of boats in the 1993 model year having both Mark IV and Gen V blocks. Gen V & VI heads will interchange. I have Mark IV heads on a Gen V block but I have been told not to put Gen V or VI heads on a Mark IV block. Hope this helps.

The heads off a 330 will lower the compression from 9:1 to 8:1 so I would not do this.
The power will drop and the MPI's ECU cal will be off...

when you mentioned small chambers what size chambers are you talking about. CC's ... as far as I recall all of GM's heads past early 70's have the open chambers all being near 112 - 119 cc's.
119 being most common.

L-29 heads are 100-105cc.

Pat is correct on both comments. Look on mortec.com and look at the specs. You need to have the casting numbers.

I appoligize for my comment. I've been out of the scene for a while and it's amazing how many things you forget. My bad...