I do not recall there being any mounts (base) 'thin enough" to be mounted on the top strap, left in place, with any 'optic' taken off, to use the rear sight.......and there are NO "see thru" types made for this application...yes it would be nice, but the 'space' is just not there, might as well use a "no gunsmith" mount, and make sure you keep ( save) the rear sight assembly for future use......I too advise to not drill and tap, as the gun will be "devalued" in this being done..............
this being said, I know you can always make something custom, like one of those "Mono mounts" clamps on to the barrel or the receiver tube of a Ruger semi auto 22 and possibly put this "clamp on" onto the forward part of the cylinder frame, and barrel, and use an 'extended eye relief' optic in this application,BUT will this "mono mount" be strong enough to absorb the recoil of a larger, centerfire gun??? hey with enough money, time and thought, ANYTHING is possible, but right now , it's just not out there being made, advertised or sold..........
come up with the "plan, details" get it "patented" and YOU may become "rich", just gotta figure it out, make it work and market it......................