Why not jump in with both feet and swap out that 250 motor with a 500?
Tons on info on the site about how to make a hybrid.
Either way, great buy for $500! Make a rebuild thread and take lots of pics. We like pics.

Q2W, he came from a Lakota & a Grizzly. We don't want to kill the new guy! lol
Great buy for $500. Welcome to the forum. Pull the exhaust & the head off to give you a better view of any obvious problems.