A suggestion I have used a few decades:
set the low - reverse clutch pack into the case dry... no planetary unit or other items in the way. Set it up eggzackly how it will operate in the trans. No roller clutch , no race , nothing to get in your way
Set the center support in place , look through the bottom of the case at the clearance. there is an opening there...
A long time accepted clearance for double sided frictions and flat steel plate is .010 per friction. 5 frictions would be .050 clearance.
If you have compressed air ... install the snap ring for the center support and test the apply through both ports
Yesterday is history.