So I thought that I had a pair of stock GM 502 HO crate motors in the boat but while doing some spring service (impellers, belts, filters, etc...) I got up close and personal with the engines. I noticed above the exhaust ports on the heads they say "world" and "merlin".

So I did some looking and apparently these heads can be a number of different designs. So I am wondering if anyone knows how to identify what exactly I have here. Do they have a casting # that will identify them, and if so where can I cross reference to find out once I find the numbers?

casting # should be under valve cover. I looked up the # on merlin site on my back up motor that came with the boat. mine had unknown merlin heads too