My understanding is that the rear sight has to be removed and the scope base affixed in that dovetail. Then you need a L.E.R. scope or Red Dot to use it. I haven't seen one in person myself, so I can't say what it looks like. I don't know if anyone has even considered a side mount for these slick little rifles.
I just picked up a M72 SS Rifle myself and have toyed with the idea of the tang sight. Guess I just need to shoot it with regular sights first to see how I like it.