seems like that's the correct SIG 226 magazine. Have you considered the 17rd 24/7 magazine? It is confirmed to work.
Taurus Mag Taurus PT-24/7 9mm Luger 17-Round Blue
Truglo universal sight
TRUGLO Long Bead Front Sight Shotgun Universal Fit Fiber Optic
Thread on sight options:
Sorry I can't help you on the screw size. I'm scared to mess with mine