Like you said in the original post, make sure the head is straight or you'll likely never get it to not leak. As far as the marine head gaskets, I think usually the only difference is they're thicker. This will lower your compression a little bit. I don't think they're necessarily stronger though. A stock replacement will be fine. :tu:

Most of the marine head gaskets i have used had a stainless steel core and fire ring instead of regular steel

Learn something new everyday. Do you know the purpose behind this?

Most marine engines are around salt water which is hard on the steel. Most small recreational engines are raw water cooled and the salt water eats the head gaskets from the inside out unless the core and fire ring is stainless.

Ah, ok. That was kinda what I was thinking. Thanks! :tu:

just wanted to thank everyone for there help got injectors pulled had water in 4 out of 6 cylinders could not turn it over by hand to had my brother do it with the starter man when that water come shooting out it looked like a hugh super water gun but engine turned over just fine no horable noises even check rocker arms with shimes everything looks good

Marine engines also circ salt water for cooling ie no rad stainless freeze plugs also

or brass freeze plugs

you do not have to remove the rockers, you just have to loosen them enough to get the pushrods out, you dont have to mess with the ajustment screw at all.

you (what everyone calls a marine gasket ) .020 oversized they run about 120.00 each

since you have already (or going to) taken the head off, I would have the head checked out, rework the seats (if needed) , I would check to make sure your head is straight and the block as well.