Thanks Tom. Your preference for the Williams answers my question. I have not tried the Ashley, but from pictures and comments, I think I would much prefer my Lyman or your Williams. My Lyman does not require tools to adjust, which is nice, and it can be easily removed from the rifle by pushing a release button that will allow the sight to separate from the base mounted on the side of the frame.
One more question, please? Does the rear sight dovetail take a standard 3/8" filler block. I notice that Marbles makes one in that size that is sold by Brownells, and I think they sell some others in different sizes. I guess the other choice would be to mount a rear sight that folds down. They also sell those in the Brownells catalog. Got any advice??