SDH is correct on the width of the 1/4 rib being critical for appearance. I don't have a Winchester M61 to look at to see how a 1/2" rib would look but narrower is probably better.
I don't see why something similar in design to a Talley ring couldn't be made up to fit a narrower base (rib) given .22 LR recoil or something like a tip off ring as designed for the approximately .400" dovetail on rimfire receivers could be made up to fit a narrower dovetail cut on a quarter rib.
I don't remember exactly how wide the bases were for the old Leonard Brownell Q D rings but they were reasonably narrow & that style of ring might work well & look nice on a quarter rib.
Just throwing some idea's out as a custom M61 is something I've never thought about before but I like the concept.
As do I-- very "Germanic" indeed.
