Open that motor up and then see what you want to do. Your gonna be out some decent bucks getting the right parts and fixing the few problems. Just finding a good tank and shock can be a chore. Hopefully that rear axle is tight and all the bearings and brakes are good too.
The thing is, if this is what he did to the outside of it, whats really going on in that motor? Aside from the head, you could be looking at rocker arms and shafts, a cam and whatever else is screwed up in there. Hopefully you have a whole top end for it.
That motor in stock form should have some decent sack.
All our government does is distract us while they steal from us, misspend our tax $ and ruin our country