I also have a ruger Blackhawk 4-5/8", it's the convertible model. It came with a 45 acp cylinder.
Two years ago I was looking for the same exact combo as the o/p. I know it's not double action but I have gotten over it. It is a very versatile gun. And accurate to. It digests heavy roger only loads with ease. I did install some trigger goodies I ordered from brown elks, very inexpensive. It's way better now.