Might aswell go for the 502 ramjet
These are using the marine pcm built for GM by holley I believe (at leasts thats what Sallee Chevy says) You can buy many different ecm's preprogrammed for your application or if you have a laptop and the software, you can make the changes yourself!
Diagnostics are done in the same way, But I dont know of a scanner (snap-on) would communicate with them. There is always the manual code extraction method.