Well firstly consider that your gun is an M11 .380; the one shown in the above photo is an M11/9 which has a considerably longer receiver upon which to
permanently affix this stock. It MAY fit on yours but I'd double check the return policy just in case.
With respects to the sight, given that the M11 rear sight consists of a flat piece of sheet metal with a hole drilled through it I sincerely doubt they simply glued on a windage knob and AR-15 sight aperture. There are various real steel sight options available including a rotating diopter drum a la MP5 series with accompanying foresight. You will also notice the cocking knob has been replaced with a low profile one to better the sight picture.
Ask yourself if these mods are worth it for a $300 CQB bullet hose, especially if it's plastic. My M11 is completely metal top to bottom and I wouldn't dare drill into it for the sake of a sturdier shoulder stock, to help me steady rudimentary sights I can barely see through to begin with. However if you insist on going "kitchen sink" on your M11, perhaps this will help you:
http://www.wgcshop.com/pcart/shopper...=GP-KIT-M11CQB