Brian and Peter, thanks for the comments.
I called the local Mastercraft dealer and talked with the owner - he said the best and safest way to remove painted boat numbers is to use acetone. Rub some on with a rag, let it sit a few minutes, and wipe it off. Will not hurt the gelcoat at all. Just don't get any on decals as the acetone will dissolve them immediately.
Just an FYI if anyone else ever needs this info