If you use the common mounts like the later ones use, youd remove the rear sight and drill and tap one or two holes under the sight leaf. They would be visible from inside the cylinder window. I guess Im a prevert, i make my guns work for me, the next guy down the line can deal with it, and on guns I truly use and like a lot, that will be after Im gone. Ive drilled and tapped various pre-64 94s and original 1886 Winchesters and several Brownings for sights and sling mounts. Whatever perceived loss of value from making any changes is offset to me by being much more valuable in use. I wouldnt alter a truly rare or historical gun, but shooter/user grade guns, I have no qualms about using them and doing whats needed to make best use of them. Ive considered making a pre-64 94 into an angle eject so I can scope it to best effect.
Ive looked for the parts a time or two, I may do it yet one day.
If you really like the gun but its not working for you now, why not make it work for you? Why let an old friend languish unused? Seems like more of an honor to keep using it than sacrilege.
Ive been considering adding scope rings to the barrel rib of an N frame 357, and leaving the iron sights intact. I have a spare barrel to do it with, the gun is older than me. Its a shooter grade gun though, I cant see the point in not using it even if it will take a little work to make it most useful to me. There are better condition ones for collectors, mines a user.