I picked up a $200 5.3 FWD LS4 to put in my jetboat project.
I have some olds 455 water cooled log exhaust and was thinking of trying to adapt them to the LS exhaust.
I put the LS headers up to them, and they are not even close, of course the joined center ports is wrong, but overall its a pretty bad match.  It would take a thick adapter to route the flow to the 455 parts.  But could I do it?  The 455 parts are nice.

I also have some 302 water exhaust manifolds, they are pretty janky lots of welded patches, but it would adapt easier.

Or I could fabricate my own using the SS headers I have.  This would be a lot more work than just port adapters.
This was my plan until I found my 455 manifolds buried in a box.

Buying LS water cooled exhaust is more than the entire boat trailer and engine, so not an option,