It helps a lot to safely install the clutch, drums and pump to have it upright.
You have to stand it on something so the output shaft isn't shoved up.
What helps on being sure the clutch drums are all the way down is to drop both drums already stacked in and a light lifting (maybe half the weight of the drum stack) while you semi violently twist them back and forth holding the input shaft.
Once seated you should be able to lift them slightly and hear a clunk when setting them back down semi fast.
Another decent way is to look at the sun gear shell and see if the tabs on the front drum line back up with the wear marks on the shell notches.
(Don't forget to put your front band in before the pump goes in.:D)
