12562934...00-up...rect...OPEN...Gen.VI 502 Marine
14097088...91-up...rect...OPEN...Gen.V 454/502 HO, 118cc chamber
I believe the heads are the same as far as performance goes. YOu should have some minor port work done to them. The HP you are trying to get can be made by accident on a 502. If you don't have to bore it .060, don't do it. Just go .030 over. Also, the carb you listed is too big. An 830-850 is plenty.