I know that Millet makes a 3 Dot replacement sight for the Gold Cup, but the rear sight is basically the same as the Elliason sight on the Gold Cup, but with two Dots.
I wouldn't mess with a 70 Series Gold Cup. In good condition they are going for $900-$1000 at gun shows and on the internet. Buy yourself a Springfield if you want a 1911 for a carry gun. You can never have too many 45s
I saw the Millet sight and I might have to try that. I already "messed" with it!
I replaced the front sight with a Hi-Viz fiber optic sight, but I could restore the gun back to original. Same thing if I replace the rear sight with a drop-in part. I bought it new in 1982 or 1983. It's condition is about 95%. A friend of mine just bought a "Loaded" Springfield and likes it very much. It looks like a good pistol for the money. But, I bought the Gold Cup to shoot, so I do!
I also have a 4" Colt Python that I bought in 1973 which I shoot, but not as much as the .45 which I shoot in a combat league.