I too am interested in the results of this conversation. It is my understand that these are the pre production pistols that would fall some where between serial number 20400 and 21700 if they were marked. I have data on 11 of these U marked guns ranging from U11xx to U32xx. If possible would you share the number of yours. Some of these pistol are very well used, but then again some are in very nice condition. I currently have U 1768 so if you want any comparisions or specific questions feel free to ask.
Robert
Robert