Bobindallas - I originally moved your post to the Colt forum, because the information you provided seemed to indicate that your gun was a commercial, and not military pistol. dsk moved the post here, as there were periods, during wartime, when Colt transferred commercial parts for military use, and perhaps your gun would fit into that category. There are quite a few experienced collectors of military pistols here on the forum, and the fact that none has chimed in, leads me to believe that your gun is what it appears to be; a commercial Colt frame, made early in the WWI years, that at some point had a G.I. slide, of similar vintage, installed. As such, it is what's often called a "mix-master", and of less value than either a military or commercial model that was intact. Still, if your father carried the gun during the war, and you have provenance, ie photos, documents, letters, or other evidence that supports the story, then the gun could have extra value to people who collect WWII militaria.
In gun collecting, a standard phrase is "buy the gun, not the story", but if the story can be verified, then it does add value.
Without a "story", your gun is probably worth $500, or maybe a bit more, depending on overall condition. As you can imagine, if the gun belonged to Chuck Yeager, then it would have considerable value, because of his fame. A gun show that I used to attend often had a display of a Luger that was carried by a local politician when he was a combat pilot in Vietnam. The gun was in very average condition, but a picture of the man, seated in the cockpit, with the gun visible, makes for a good story, and with the pictures, letters, etc., can make the gun more interesting and valuable.
