Assuming that the CZ magazines are dimensionally identical to Ruger magazines, he would only need to cut a catch hole, at precisely the right spot, into the front of the magazine body.
One could compare the two representative mags. side-by-side and see if the lines, angles, and dimensions match. I have Ruger mags., but no CZ specimens.
However, I'm thinking that CZ mags. are 'angled' more than a Ruger magazine, and that would create a problem in the way the top of the magazine is oriented in relation to the feed ramp, chamber and action of the gun. That is to say, the magazine would probably fit in the magazine well, but the feed lips would might extend upwards too much at the wrong angle and make contact with the bolt carrier and the cartridges would be fed at the wrong angle to enter the chamber as well.
Again, as I said previously, if they are the same all that would be required is a new catch hole. But if there are even minor differences, he would probably experience reliability issues. It's worth a shot, though. He could get a cheapo 10 rd. CZ mag. and experiment without really any risk.
As far a modding the carbine, I don't think I would. If he alters the gun, then he might just render it totally unsuable. Screw up a magzine and he's only out a few bucks.
There is a company that modifies the magazine well on the Ruger carbines to accept different manufacturer mags., but I don't think a CZ conversion is offered. I can't even recall the company that does the work, come to think of it. I'll poke around and see if I can find the company.
Good luck in his endeavor.
