My buds 94 is getting rebuilt as we speak, could have swore he said it had flat tappet!

Yup, 94 should be Gen V. Flat Tappet.

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yep,91 through 95 were gen5.

The Gen V 502 Mag, had a 220/220 115 LSA flat tappet. The Gen 6, had a 224/224 115 roller tappet.

As far as I know, the MPI 502 MAG, whether it had either cam, was rated at 415HP.

Joe not related to this thread but which 502 used that small roller like .463 lift and real short duration. I'm just curious.

That was the gen 6 502/415hp mag. 224/224 , 483 lift i believe.

Motors are '99 gen. 6 with roller cam. The head's part number is 12562934. everything appears stock. The exhaust manifolds are stock cast iron mercury. They have a 4 inch spacer between the manifold and the riser that my other boat does not have.
I bought this boat as a non running project, so I don't know all the history of it. One of the motors got water in the oil and was left for a while, the cam and lifters have rust pitting and need to be replaced anyway, so i figured I would upgrade both while I am in there. If anyone knows of a bigger cam i can use with the stock exhaust that is what I would use. However It sounds like the consensus is an exhaust upgrade is where I would have to start. I probably will, but wanted to kick that can down the road and get it running for now.
Why would the H-beam rods not be better? Having two different rods in my engines would cause my ocd to kick in a little, but sounds like the oe ones are good and money would be better spent elsewhere.
Someone mentioned Wisco pistons, Are they better? and why?
Looking at valves, I noticed there are larger ones than what I have, would there be any benefit of going bigger at this level?

Thanks for all the replies, this is just the kind of info I was looking for.

The reason one engine probably has H beam rods, is its usually a wise investment, to replace the original rods when rebuilding the engine. Not that the OE dimple rods are bad, but by the time you pay to have them rebuilt, you're almost at the price of a set of new H beams, that are a bushed floating design, and overall better rod.

Would you notice any performance difference with one engine having H beams, and the other I beams? No. But, I also have ocd when it comes to that, my engines have to match in every way.

First thing I would do with those engines, rebuild them to stock specs, and simply put a better exhaust on. Unless you want to get into a different cam, custom ECM tuning, converting to an adjustable valvetrain, and so on.

It's kinda funny when you guys mention the OCD and exact matching parts etc. It's easy to sit back and say no biggy run what you have but when's it comes right down to it in my world it's kinda like wearing two different brand of white socks. Even though no body would know but myself it would still bug the chit out of me. MT U pretty much nailed it. I always felt good using my own reconditioned rods only cause I knew what I had and that it was worthy of the process. That was back before the H beams have become pretty affordable. I just wouldn't use any H beam as all.