I'm not sure I understand what you mean by "no way it can be installed with the slide stop in place" - you can't install the .45 top end if the slide stop is IN PLACE, either. Your description makes me think it's not the slide stop you are referring to; "the rod extends rearward" makes it sound like you are talking about the ejector. The original Ace was not intended as a conversion, and I don't know if it is even compatible with a standard Government Model frame. There should be a lug on the .22 barrel, through which the slide stop pin passes, to retain the barrel/slide assemply on the frame. No lug? No hole in the lug for the pin? If it is the ejector that you are referring to (fixed to the top, left-rear of the frame), then you might be able to remove it to fit the Ace slide. Is that serial number 7000 or 70000? Serial 7000 might be pre-WWI.