Irunguns for magpul g36 mags. Mod each mag if you want the gun stock.
Easier just to grind out the tabs, then he can use any magazine. I did both, when grinding out the tabs, you just have to take that thing apart as much as possible, good lightening, dremel and patience. Or let a gunsmith do it.
The "problem" is that the Magpul are 30 rounder and therefore very long. But they are good. I bought quite a lot at some time from IRG and sold a bunch on gp for a profit.