yup its used for zeroing (the theory being each persons eye sees a certan point on the graph thingy and you just rezero onto that) no idea what its called
no,i mean just unscrew the cloth you have on there and replace it with the real deal one,dont even have to touch the internals,iv seen it done somewhere god only knows where lol but im sure it can be done
why bother going fancy when plain stock does the job just fine ? its not exactly fancy the erganomics of it are far better than that of the para stock along with the adjustability