The 8-port is quite a bit stronger. I think only the piston and sleeve are different between the 4-port and 8-port. At least those are the only differences I could tell between mine.
What are you putting it in? The .15FE has a threaded crank while most big-blocks (like the Hypers) have SG cranks. The big-block engines are quite a bit larger than the .15FE as well, it's definitely not a direct bolt-in.