Nice work Rasyad,
I just did almost the same thing, drilled and taped a hole a 6-32 hole in the stock release button (This is one hard piece of steel).
Reassembled the stock release button and spring positioned the stock to the length I wanted
I cut an old drill bit approx 1/2" in length and dropped it in the hole.
Installed a 6-32 x 3/8" set screw and tightened it down.