They look like Millett sights, and if the front is a Dual-Crimp style, you are sort of stuck with it. The D-C uses two round rivets that are staked in place, and the size and spacing of the holes leaves you without any other options unless you want to weld-up the holes and start over again. I used a D-C sight for years, and there's really nothing wrong with them, as long as Millett makes a sight that you like.