1. You can tell the selector forks apart because they have slightly different radii that follow the correct gears on the main shaft and lay shaft. No one tells you this. All is said is to use the right ones.
2. Put the gear cluster pieces in individually instead of as one big lump as they show in the manual. So much easier. Start with layshaft and its gears and its selector fork, put in the main shaft selector fork (behind the layshaft selector fork), and then each piece of the main shaft gears, followed by the mainshaft.
3. The manual is worthless. Wes White's video is the best help. By the way, units have thrust washers that the pre-units do not. So don't freak out for a moment like I did.
4. When doing a test assembly to make sure it shifts, tighten up the kickstart gear. Hand tight should be fine. If you don't the gears will bind up.
5. Don't tighten up the sprocket before tightening the kickstart gear. You won't be able to get enough mainshaft teeth to tighen the kickstart gear to. Tighten the sprocket last.