It apears when you zoom in on the ACE adapter it is held on with two hex screw.
Look at how that uzi pistol is Drilled & tapped in this thread.
I recent aquired a nice Uzi pistol from the original owner. These hole in the rear of the receiver have me buffaloed. Any idea what they are for? Both are threaded and in the middle set of indents. Any help is appreciated.
uzitalk.com
Or you could try finding a UZI PRO brace and replacing the brace with the stock.
They are the same hing pin between the two.
IE: A mini/ micro stock will fit on the PRO by just removing the C clip and swaping them out at the hing pin. Or the other way around.
Remove IWI brace from the tube and replace it with the stock,of your choice.
All you would need to do is slap a AR stock on where the brace attaches.
Looking at pix of the PRO brace it appears to be held on two screws also.
You might get lucky there and just be able to swap the brace tube for a buffer tube.