I think you're right. I have a book at home that shows Ford holding a Colt "Frontier Model" (as they were originaly called) and the caption says that it was the revolvwer used to kill James.
It's the Time Life series on the Old West. It shows Robert Ford holding a SAA Colt in his left hand (he's sitting in the photo). THAT book claims that he was posing with the gun he used to pop Jesse James in the back of the head. The book could be wrong (it's Time Life, after all), but it does claim that that's the gun. In any event, I'd want documented proof, before I paid big $$$$ for anything like that.
I own a Remmington Pepperbox .32 derringer that was made in the early 1870s. MAN, if only it could talk!!! The damn thing still fires .32 rimfire rounds that have not been made since the 1920s. I have a box of .32 rimfire "shorts".