The higher front sight is for the stainless .45 Colt Blackhawk. It will only work on a stainless Old Army where you can drive the pin out and replace it with the higher one
However, there is bad news. When I tried to order the Blackhawk blade about 7 mos. ago, they didn't have any at Ruger and most likely still don't. I eventually had to use 1/8th inch thick piece of flat stock and cut a piece, reshape it, tap a hole and pin it. I also cut the notch on the rear sight down as far as possible. Now I have one that is plenty high and still have adjustment left in my rear sight. It is probably the way you'll have to do it too. It wasn't difficult .. just time consuming.