Did the engine just plop straight in face to face or did you have to pull it together with the bell housing bolts?
Have just had a thought.
The torque converter engages with, and drives, the fluid pump. If the TC is empty then it will spin internally and not produce any drive to the pump. No drive to pump = no fluid into the TC = catch22.
A grownup will be along shortly to tell me how wrong that is.
Steve