Most of these 44 Rimfires got their barrels cut and also were converted to a centerfire cartridge. Over the years I have had 8 of them, with most of those found in Mexico. They were numbered in a separate serial number sequence from the other Colt SAA’s. The serial numbers range from #1 to almost 1900. When many of these didn’t sell, Colt later altered to 22 Rimfire.
I can tell you right now that the hammer is not correct, and the firing pin doesn’t look right either. The frame slot was welded up, and a very crude job of re-cutting the slot was done.
I never saw a serial number 50 on the cylinder, but would bet that it has been replaced. The chamber appears to be 44 RF, but I would have to see it to rule on whether the chamber is like it would have been originally.
The seller doesn’t give a good picture of the barrel address, but it appears to be italic, which this SN would likely have. I am not seeing the expected marking on the bottom of the barrel, but would like to view a see-thru-the-bore picture to judge whether it was 44 RF or not. It may even be a 45 barrel, from what can be seen. The barrel shows pipe wrench marks, and was cut down from 7-1/2".
From what I can see, the frame, trigger guard, and backstrap are probably original to the gun. The entire gun looks “warmed over” with polishing and artificial age. Of course, the grips have been replaced.
That old sales receipt doesn’t add anything of merit, except for providing an idea of when all of the above work was done.
NOW after bothering to read the seller's description, I see that the barrel is probably from a 45 Colt U.S. Government gun! The "P" is still there, but the "A" may be worn (or filed) off.