We learn the most from our mistakes. I rebuilt the p.s. gearbox in my 65 Dart and it works fine. Long ago, I tried rebuilding the one in my 69 Dart and it wouldn't work. I gave up after several attempts. The trick is that after assembling all the internal disks, you need to hold the input shaft tight CCW as you insert the innards until you get the top spanner nut tight. If you don't keep them tight, they can pop out of position, which was likely my problem before. I doubt your parts were damaged, just mis-aligned. There is a special tool for that large spanner nut, but I just rigged 2 screwdrivers and a pry bar as a home-made spanner wrench.
