The cam gear does look like it is meant for reverse rotation. You might be onto something with the marine cam. It might be a left hand rotation marine engine.
If so, replace the cam, timing chains, and distributor gear for typical automotive stuff and rock on. You don’t have to worry about replacing the crank as marine engines just run a “reversed” firing order.
If it was in fact a marine engine, I'd take the disassembled bock and have it thoroughly cleaned.