Hi Gary,

The screw size for the Lyman 48 is a 6-48, I don't know the
lengths off the top of my head but if no one replies by this evening, I will get out a sight and measure them.

I have a 1903 that was drilled and tapped for a receiver sight.
When I went to try a Lyman 48 on it, I found that the front
of the sight block interfered with the bolt. A Redfield 102
like you have on yours worked fine. You may encounter similar
difficulties. I hope not.

All the best,

PhysDoc