I am currently working on the same problem with a 77 express. Here is my experience so far:
1. Make sure that the bearing mounted in the left case cover is in good shape. If it is sloppy and worn out, the ratchet starter will sit at an angle once it is under load and prevent installation.
2. Install the starter gear as described in the manual with the punch mark on the gear pointing where they tell you.
3. Put the kickstart arm on the shaft and rotate the gear so that the return spring engages and the two lobes on the gear are clear of where the starter stopper will sit.
4. Keep tension on the starter lever while you or a friend installs the starter stopper.
5. Release the kick start. There should be some tension on the starter chain at this point and the lives on the gear should rest against the stopper.
6. Install the ratchet spring around the collar where the ratchet sits. One leg of the spring goes in the small hole on the plate that holds back the big bad evil spring of death.
7. Install the ratchet lever and swing it around so that it catches the other arm of the spring and ends up being pressed against the starter gear.
8. Push on the kickstart lever so that the punch mark on the gear is lined up with the the ratchet arm. For me, this was about two or three teeth away on the gear at this point.
9. Push down on the starter gear and ratchet arm to be sure they are well seated and that the ratchet arm is lined up well with the gear teeth. Don’t put your fingers anywhere that the chain will cut them off if the thing releases.
10. Be sure that the release lever is pushed toward the rear brake. Carefully put the cover back on. Turning the flywheel slightly as it gets close to being together. As I am installing the cover, I position the case so that I can look down and get a visual on lining up the ratchet, starter shaft, and the shafts on the two drive gears. It takes a little wiggling at first, but it should go.
11. Listen for a “ping” as you go. If you hear something release, take it apart and reset the ratchet arm. Do this like 50 more times until it works.
A side note: I believe that my ratchet spring is deformed and therefore has a tendency to ride up onto the shaft of the ratchet arm, causing the ratchet arm to sit farther away from the L case than intended. I believe this may have been making my life more difficult resulting in multiple attempts to reassemble. I think, but have not tried to install the ratchet arm in the loaded position before everything else (add it as step 1b in the list above) My reason is that as I swing the arm around, I must lift it to clear the starter gear, thus allowing the ratchet spring to wrap around the shaft instead of the collar that extends from the L case and receives the ratchet. I think you might be able to swing the ratchet around and use a small bolt or screw placed in one of the other holes in the big spring cover to hold the ratchet back while installing the rest.
I hope this helps someone.