I don't know why 6 cyl. engines didn't have a dwell door.
If you have a door on your cap, when the dwell is properly set and the timing properly adjusted. The next time you replace your points, and you adjust your dwell (running) you won't have to reset your timing. (check it anyway)

I didn't do it, no one saw me do it, you can't prove anything! "Bart Simpson"