Need 904 assembly help!

I would suggest removing the clutch discs and steels from the high/reverse drum only, leave out the intermediate band, leave off the large pump seal and gasket, then assemble everything else and see what happens. If your clearances are correct, your getting hung up on a clutch disc. If it binds up again, take out the thrust washer that is between the two clutch drums. If it binds again, put that washer back in and remove the small one between the forward clutch drum and gear sets.
Bob, thanks for the suggestions. Last night(!) I put it together again without the output washer, and it works. So , I will make a custom washer maybe .040 ,which will give me an extra .028, which might make it. If not, an extra gasket in the tail shaft area will get me another .010.