Jim, That small screw holds the top lever shaft in position in it's fit in the trigger plate housing. The screw is tight, but when you turn the top lever to open gun this screw actually loosens and then when it is closed it tightens back. The only thing it does is to keep the top lever in it's fit and to stop the lever from "riding up". The screw is only 1/4" long.
Too far to the right could just be wear on the rotary bolt as it has a curved surface that the rib extension locks into.
Sad to say I will not be at the Vintagers, good Lord willing next year I hope.