OT, but please indulge me. Jerry, your post jarred something in my memory. I wasn't present, so what I'm about to relate to you is third-hand.
Anyway, I was told that at a shooting match at my club about 20 years ago, a gentleman had brought a beautiful Colt SAA, presentation box and all, chambered for the .455 Eley cartridge.
Even though at the time I was a burgeoning Colt SAA nut I never followed this bait, thinking it was yet another apocryphal nugget so prevalent in the world of old guns and collectors.
So now, years after circumstances forced me to sell all my Colts, I put forth the question, especially to our British friends. Anybody know of a production ColtSAA of this ilk?