A cased set of the following items has been brought to me with the question I hope to find help answering here: A 1911A-1 commercial frame with a serial # in the middle 7000 range. It has a checkered arched housing, and a slightly widened hammer spur. Two .45 barrel/slide assemblies, all Colt marked. A .22 ACE slide barrel/assembly (no service model markings), without the floating chamber, with 6 fiber washers on the recoil spring guide, and without any clearance cuts that would allow the slide to be mounted with the normal .45 slide stop in place on the frame. I should emphasize that everything seems to be of similar age and is all Colt marked. The present owner knows that the set dates from 1943 or earlier. The question is, is the .45 slide stop removed to install this ACE slide and then replaced when mounting the .45 tops? The .22 barrel has a bar or rod which snaps into the left side breech area, and extends rearward into the space that would be occupied by the slide stop. Remember that there is no way the .22 slide can be assembled with the .45 slide stop in place. I would like to know how these options should be set up to function properly and safely. Is the .45 slide stop there just as a hold open, or would there be a safety issue firing the gun as a .45 without it? Any help that is offered will be very much appreciated.