It really depends on which mount you get. There are two types. One you totally remove the rear-sight base and use the dovetail that is underneath. Those usually require the use of a torch, since most are soldered in place. But that is the strongest mount. The other replaces the sight leaf. There are a lot of different ones for that, some good, some garbage. The only one I know is good can be found here...
http://parallaxscurioandrelicfirearmsforums.yuku.com/forum/view/id/116
It's a bit pricey, last I looked somewhere around $70. But it works.
As for the scopes, you have to use a long eye releif ( aka pistol ) scope. While its not hard to find a good one, they tend to be pricey as well, and usually not very high magnification. That said, I do know several people that have modded their Mosin and Finn Nagants that way and they make for excellent shooters. A friend at the range has a nice Finn and a 91/30 that way that he uses mostly for target shooting, and a M38 that he uses for hunting. Only 4x scopes though. He found a 3-9x, but couldn't see paying 4 times for the scope as he did for the gun.