I’m having the same problem with a 1960 18 horse. I’ve taken the powerhead off the exhaust housing and tried a MAP torch on the driveshaft , but no joy so far. Maybe two torches simultaneously to get it really hot will help. I’m also thinking to borrow my neighbours air chisel, and affixing a platen of steel to hammer in the vicinity of the crank. All this while suspending the powerhead from the driveshaft.
