when you dropped the transmission, did you pull the shifter? I have on a couple of times been able to set the shifter in wrong, and not be able to go through the gears.
Disconnect the driveshaft. Pull the shifter. Play around with the shifter stuff in the tranny till you can turn the back of the transmission, indicating you are in neutral. Replace the shifter ball and try to go through the gears again. This should take all of 10 minutes to do.
