The wrist pins would be my first question also. But don't jump to conclusions---they are easy to check for looseness. Remove both spark plugs and use a screwdriver to follow the pistons down as you slowly rotate the flywheel. Just follow the piston, don't push. When the piston is half way down, stop turning the flywheel. Now, give a push on the screwdriver. A clunk and movement indicates wear. A microscopic movement is normal and ok. 1/16" of clunk is on its way to the graveyard or rebuilding. Or it will run till a wrist pin falls out and goes boom.
BTW, the rod bushings were not the whole problem. The real problem was the wrist pins were too small in diameter and would beat the hole in the pistons to death. The newer parts include needle bearings, pistons, con rods and larger wrist pins. You have to replace all or nothing.
