Well I can't say it hasn't been interesting, this trip I've taken to learn more about my Colt M1911A1 pistol. Jim Cutting is right, the slide is a 1944 variation replacement slide that has been parkerized (still don't know how to tell a parkerized slide from a non-parkerized slide). Here are the clues I've learned from Jim and other people:
1.The pistol had been parkerized.
2.The slide has a dark heat treatment line along the forward half.
3.The texture of the finish is not original.
4.The Colt's big belly is reflective of Type 9 in book illustrations, and this is found on other 1944 pistols.
5.The front sight is a Type 3 -- the original oval shape was modified to one with a straight serrated slope to the rear; this began in 1943.
So while the frame is a 1938 frame, the slide is most likely a 1944 replacement slide.
Thanks to all who have been on this journey with me. It was interesting!