So what might I have done wrong that would cause it impossible for me to shift into reverse? No grinding or anything like that - it's as if there is just something blocking the stick from going into the reverse slot. 1st through 5th works great, btw, and I was able to shift into all gears and drive before I took it apart.

Great post - still helping 4 years later! So, I got into the tranny because I thought I needed a new throwout bearing, but discovered that the noise I was hearing was coming from the bearing on the input shaft (the one furthest from the engine). I didn't do a total rebuild - I just got a bearing kit which replaced all of the bearings and the washers. I cleaned everything pretty thoroughly because what had happened with the bad bearing was the plastic cage holding the ball bearings in place broke, and i was chasing its pieces all out of the oil channels and nooks and crannies and such. Any ideas? If you still follow these forums, your help would be most appreciated again!