I wouldn't bother with the trans. unless you have to tear into it for a mechanical issue.  These old tractors are just going to leak a bit,  most of the shafts in the trans. never had seals, so it will leak even after all the labor to reseal the lower pan.  I just went to the farm store and picked up the heaviest gear oil I could find and mixed it 50/50 with lucas oil additive,  it ends up about as thick as honey.  You should need about a galon of each, the gear oil was 180wt or 150wt, I don't remember for sure.  Best of Luck!!