Model 600 tractor

Attempts at cranking, with the starter, or with a bar on the front of the engine seem to worsen the seezing.

1. What would typically be a weak point in this engine?

2. How can the camshaft drive gear be removed with minimum risk of damage? I have a 3 leg puller but can grip only the outside edges of the gear. The gear flexs slightly and I don't want to risk damage. This tractor has the early type of gear with center bolt and keyway. How much force is acceptable and how much heat if any can be used.

3. I feel that removing the gear will allow me to determine where whether the trouble is in the crank/piston area or in the valve train.

Does this approach seem okay?

Thank you, Bill