Re: Mosin
It has been done, but why you would put money into a mosin is beyond me. It's just not a precision platform.
I'd keep it as is since it's pretty much the most rugged thing out there as it is. Use it as a plinker or a truck gun, and pick up something else to customize.
Large ring mauser 98 actions are great cheap starting points. Aftermarket versions are great too: Charles Daly mausers, interarms mark x, CZ actions, rem 798, etc.
Cruise your local pawn shops and keep your eyes out for a cheap rem 700 (or the older 721/722 versions), mauser 98 variants, winchester model 70's (with claw extractor), or possibly even 1903 springfields. All these would be a better starting point than a mosin, IMHO.
good luck!