So, what all did you have to do to get it to fit? Was it more than just the square corners inside the frame?
In the second picture below you see the phantom slide, upside down, muzzle on the left. Starting at the red circle and continuing down the slide is a rounded radius. Instead of being at a pleasant 90° angle, it is like a 90 with a rounded corner.
As the CZ 75 frames have a nice sharp 90° edge (see picture 3 red line), the slide will not enter the frame rails starting at the slide tunnel. The rounded radius interferes, this is seen in picture 1. You'll also notice a lack of rear sight...
Option 1. Mill the rounded radius off the slide. I don't have access nor knowledge to do that. Of course both CZC and CGW were willing to do the work. Refinishing the slide would also have to happen.
Option 2. Break the edge of the frame rail with a file. Giving the frame rail edge a nice chamfer seems like the best idea given my lack of machinery and that the work is hidden inside the frame. Not entirely necessary to refinish the frame. This is the method I chose.
Now let's look at picture 3. The red line on the right is the total length of the frame rail edge that needs to be chamfered to match the round corner of the slide. Using some files I broke both edges and tested the fit until the slide would return completely rearward. The slide tunnel would clear the frame, however the fit was exceptionally poor. The slide tunnel is too wide conpared to the interior width of the frame... It wouldn't slide freely. In picture 3, the yellow area bordered by the red edge all had to be reduced on both sides of the frame.
You'll notice that the slide finish in picture 2 shows some light scuffing denoted by the yellow arrows. I'm not too worried about that, but the circled area was wearing down the polycoat enough to demand more attention after test firing.
I did all fitting by hand and used Super Blue to protect the metal. After reducing the right side of the frame to mitigate the rubbing, I'll reapply the cold blue and do a couple more coats. The pictures don't do it justice, it turns out black.
FWIW, all my polishing of the internal parts will get the Super Blue treatment in the next couple weeks.
TL;DR what was initially thought to be quick and easy did not turn out that way. The slide is smooth, but it took many hours to get there...