Have you pulled the valve cover and checked the operation of the valves? Stovebolts have a nasty habit of sticking valves in the guides and bending pushrods. If old, stale gasoline from the fuel tank ends up in the engine, gummed-up valve guides can happen after a very short time even if they were clean on startup. Always use clean, fresh gas from an auxiliary tank to ressurect a vehicle that's been parked for a long time.
Jerry