I know that the CZ USA custom shop was doing this work because I saw them at the Shot Show in Vegas several years ago plus I have a CZ550 in .416 Rigby that has been fitted with a pop-up aperture (however, this rifle is still in the USA and I am waiting for it to be shipped out).

However, when I recently wrote to CZ USA and asked about this work the reply I got was that they don't do this work and have never done it!!!! So I am quite confused by that reply and my .416 Rigby is certainly evidence to the contrary on that reply!