There is another way to do the rear sights like that is not as expensive a custom job. Krebs also sells the A2 sites alone. You can attach them yourself if you have the ability, or it is a pretty simple job for any decent smith. The dust covers are usually very tight, so it doesn't change zero, but if you are concerned then Krebs sends a little kit that attaches to your recoil spring retainer that tightens up the dustcover to the frame. That is also a pretty simple thing for most smiths to do. The whole site assembly runs like $50 from Krebs if I recall correctly, and installation should not be that expensive.
Do a search under my name and Krebs, I posted a review of the sight setup, and I really like it.