Pachmayr and now LPA sold a rear adjustable sight which didn't require machining, just a sight-pusher tool or a brass hammer. Supposedly designed for use with modern factory front sights... Unfortunately most of whats left out there requires scrounging through new/old stock bins.
I'd say talk with Robar or a couple local 1911 'smiths (get pictures of past work/references) and spend for what you want. Money is replaceable.