Whats the difference between the 502 MPI and 502 EFI if there is one?

The EFI's are the older version. They use the VST system with a mecahnical fuel pump and vst tank and electric pump.
The MPI's use an electric fuel pump and cool fuel system.

Pretty sure, the engines also have different cams.

The 502 EFI became the 502 MPI in 1996 when they went to the Gen VI block, so roller setup. Unfortunately, they still used the VST and belt driven fuel pump in the MPI for a while. The cool fuel came later. The difference is Gen V vs Gen VI. The rest is the same.

Yup. Thats what i got. A 94 502 EFI. Its got the Mech pump and the VST. The boat motor only has about 50 actual running hours. Boat was a yard find, been sitting for years. Thanks for the info. Do you if there is a procharger that will work with the EFI.

Same, when we had my 98 mpi and Christian's 96 efi motors apart last winter the long block were all the same.

Sure, good platform to procharge, all forged internals, fairly low 8.75 compression. Make sure your valve train is ok after sitting for so long.