What you do is install the collar on the bottom of the shaft (just above "slot") and tighten it just enough to where it will stay in place on the shaft, but can still be moved fair easily. Do not make it too tight or it will not move during the next step. Also, go ahead and put loctite on the set screw at this time. Once the collar is in place, install the distributor in the motor and tighten it all the way down. The collar will slide into the correct position. Then all you need to do is pull the distributor, tighten the set screw, and reinstall.
I robbed the photo off this site