By your description, your hopes are not realized, the gun is heavily modified.
By your own account, it sounds like they screwed half moon clips to the rear face of the cylinder to headspace .45 Colt.
They would have had to have reamed the chambers for the longer cartridge unless it is one of the earliest Colt 1917s with bored through chambers. The reamer would have cut some off the clips to bring their notches to the radius of the cartridge body instead of the size of the extractor groove of the ACP.
The reason it does not extract properly is because the .45 Colt has a very narrow rim. In its original home, the Single Action Army, the rim ony served to headspace the cartridge against the firing pin strike. Extraction was by side rod.
The 1909 Army cartridge is the same as the .45 Colt except for a wider rim for use in the double action simultaneous extraction New Service revolver. The gun the 1917 was based on. You are not going to find any of that ammo, it was official issue for only three years, 1909 to 1911.
The gun is probably safe, .45 Colt is loaded to lower pressure than .45ACP, but it is not original and I don't know what it would cost to find and have fitted an ACP cylinder. Probably a lot. It would likely shoot clipped ACPs if you took off the attached and modified clips but accuracy might suffer in the longer chambers. Or not.
I would consider it a novelty to be shot on "ceremonial occasions" and move on with the knowledge gained.