Perry:
I'm not familiar with the 3hp, mine have been 18hp+. First check the compression -if it's way off factory specs, junk it unless you're into major rebuilds. Get youself a service manual and start going through it. Coils, points, condenser, wires, fuel filter, water pump impellor, these are the items that you'll want to replace unless they look like they have been replaced recently. For the most part, if the compression is good and the physical shape is decent, I don't see where it wouldn't be worth fixing up.
They are a pretty simple setup and many don't have the running hours that you would expect. I have a 57' Johnson 35hp on my duck boat, runs like a champ.
Good luck!