Jim;
I am not familiar with the Union Firearms doubles so don't know if this would be applicable or not. Some years back I bought an H grade Lefever parts gun which would not close. Investigation revealed the trigger plate screw had been replaced with one which was too long & it protruded into the slot in the frame for the cocking hook. On trying to close the gun the cocking hook would hit that screw & prevent it going to the bottom thus preventing the gun from closing enough to bolt up. I removed that screw & ground off a couple of threads & it closed & bolted fine, in fact, was quite tight & on the face, even though the top lever was well over to the left.
