Performance is not really a factor that comes up much with used engines. If you are going to haul firewood all summer, a rebuild might be needed. If you are just cruising around town a few months out of the year, then follow through with the cleaning, new gaskets and seals. Blow-by from wear and piston slap is real possibility with worn cylinders, but then these engines pretty tough and can take a lot of abuse so who knows, it may not cause any problem.
Rebuilding is expensive, $3000 range plus or minus depending on your location and parts availability. Are you willing to part with that much? Will it run that much better, I doubt it.
Measure all the bores at a few depth and head over to your local machine shop. Talk about the engine and look around to see if you feel comfortable with them. Ask about old engines and see what they know. A lot of shops only deal with late model stuff.
Joe
