If you still happen to have your old jug of glow fuel, that's a great solvent for getting that gummy castor residue out. I've cleaned out completely seized engines with it just by soaking for a day, working the engine a bit, then soaking for another day and turning it a few times. The methanol will penetrate into all the little crevices and free the engine up. The spraybar and fuel passages in the carb should be cleaned out by hand though, and all the orings should be replaced. I'd try the soaking method first before tearing the engine down. Not that new bearings ever hurt anything, but if the engine cleans up and turns smoothly there's no need to go further.