So, bascially if you have a USGI 1911A-1 frame with the "FJA" inspector's initials on the left side above the magazine release button you have a Remington-Rand or Ithaca mfg frame. If the slide is "Colt" [or other mfg than above] you have a mis-match or mix-master pistol. This commonly occurred if pistols went into an military arsenal armoury for servicing. Look for a "SA" or "AA" stamp on the right side of the frame indicating this.
Common inspectors initials for WWII vintage Colt mfg 1911A-1 frames are "GHD" [Guy Drewry] and "WB" [Waldemar Bromberg].