I have the same tractor,
the distributor shaft top bearing could be worn. This loose play will make it very difficult to adjust your points and keep them set.
Take the rotor button off and move the distributor shaft back and forth. The back and forth movement will determine the level of wear in the top bearing.
As for as getting out of time, you may not have tighten the distributor holding bolt properly.
Let us know what you find wrong.