My father has a 96 29' fountain fever with the 502 mpi black motor with 203 freshwater hours on it and he is thinking of dropping a 525 supercharged motor in place of the 502

What you think the 502 is worth? And would it be worth dropping a 525 sc Motor in there?

Would be great. The boat would lighten up nicely. Could turn a bigger prop. Would feel very different with 100 more hp. Do it.

What you think the resale on the 502 would bring to fund the 525?

Well there is a 502 now for sale now here in the swap shop for $2500. I see rebuilt ones for 5-5500. So I would say 3500 maybe 4000 on the top side???

As for a 525sc, your going from fuel injection to a carb... Me personally, Im not a fan of carbs, I like the ease of EFI . When was the last one installed in a car from the factory? What about a 575sci .

Or forget the swap and put a super charger on the 502. This way no engine swapping, and depending on boost levels you will be 640-700 hp on pump gas and EFI...

Yes, the 502 magnum is a great base for supercharging. It would easily get you that 100+hp and still be reliable for much less cost. Great idea. That is a Gen VI motor and with that few hours is still in good shape and could handle the supercharger.