I have to agree with Jake with regard to customizing,
The Mosin Nagant used to be a $60 fun gun and they are fun to shoot, but if your goal is to make it into a modern sporting rifle your journey will end in disappointment.
This is not a "purist" vs "bubba" argument, just speaking from experience. Here is why:
-The Mosin Nagant has a split rail receiver, so near impossible to mount a peep sight or drill and tap for a "normal" rear receiver scope.
-Most over the counter bores vary in size from .312(good) to .315(very loose), so when shooting factory or surplus ammo your groupings may suffer.
-After market parts are available, but price adds up quickly. You can end up spending more than a brand new Ruger American and still have a 2 moa rifle.
Now if you just want one for nostalgia reasons, try to find an Ex-Sniper (google for details) and then scope it with a PE or PU scope and you will have made a repro sniper. This will give you more resale value and serve its purpose (adding optics).
You can leave a 91/30 as is and still have fun, just keep your expectations realistic. I do have a blast when I take my Mosins out, just hitting steel at 300 makes my day.