Randy, ther serial # on my gun is IBUI, according to the information that I found on the net the letter only system was used from the 1940's until about 1956. Also, the letters correspond to numbers. The corresponding numbers on my gun would be 2672 and your gun would be 2677. Five (5) guns apart,so your gun is almost a twin. Very interesting and probably explains the similar quality. I will try to find the web site where I got this information for your reference.

Regards,

Max