I acquired a Colt Gold Cup Series 80 that had many of the same problems as your 1911 does including a non-working bevertail. Numerous after market parts had been installed on my GC by a part installer (as opposed to a gunsmith) in Georgia.
I had my gun worked on by a local South Florida gunsmith, Robert Munck. He fixed everything including all of the after market parts because the guy that I got the gun from did not keep the original Colt parts.
Robert is the gunsmith for Pompano Pawn in Pompano Beach, FL.
Their address and phone number are:
1301 West Copans Road
Pompano Beach, FL
Good luck with your repairs.