John, The original DW pad would be hard to find, they were also used on some shotguns 1920-30's so maybe our shotgun friends who read this could help.
I would try to find a Lyman 48 base that fit the 52 and try a 125 slide and see how it works, the groove in the wood does not look long enough for 150 slide but the picture sure shows a long one. If you get to that point I can send you a 150 slide to try out and see if it fits.

Do you have a closeup picture of where the Redfield was?

MP Sadly Deceased as of 2/17/2014