I am looking to do some custom work on a family member's Mosin-Nagant. Some pictures from ya'll would be great for ideas. Some of the stuff you see on the grand ol' interwebs is a little excessive.
If it is a nice looking original gun? I'd just shoot it. It's not the greatest starting block for a good sporter. But if you just have to there are options for stocks, scope mounts (usually requires bolt handle mods) Triggers, mag options etc...
Biggest issue is you will still be stuck with a pencil thin barrel and to will have enough money in it that you could have bought a new 700 or other bolt action. And it, no doubt, will out shoot your sporter Mosin.
If money is not an issue, then I say go for it! Have some fun. Just google sporter Mosin and a ton of stuff will come up.
(sarcasm implied. Please take all medical precautions and talk with your doctor before clicking on the link above. Please seek immediate medical attention if you look at the mosin in the link above and find it interesting. Especially if you tell your friend "hold my beer" before working on your gun.)
I refurbished my first Mosin, but kind of wish I would have left alone and just cleaned it up. Granted it was only $99 at the time and only in fair to good condition anyway. Thanks to it I came across M39's, which are much nicer.
If you are not too worried about resale, refinish the stock. You can really clean them up and if you are careful, preserve the cartouches while doing it. Some walnut stain and several coats of linseed oil will really improve the look of the whole rifle. After that, maybe do a drop in trigger kit and possibly bed and cork the barrel/action. It will never be a long range tack driver, but they can clean up really well if the gun is in good condition to begin with. When done, it will have an original look to it too.
For real long distance (which I lack experience) I am sure a sporter wouldn't be a tack driver. However, for a number of us who just punch holes in paper for fun they are hard to beat. A few years ago when they were super cheap and plentiful, I built a sporter for my dad as a Christmas gift. Started with a 91/30 went with the ATI stock, bolt handle kit and scope mount and bedding pillars. Then I used a piece of pvc pipe and sandpaper on the stock to free float the barrel (just enough to run a dollar around the barrel). Drilled the reciever for the scope mount (careful, broke 2 cobalt bits), modified the bolt handle per ATI's instructions. Mounted a Weaver Nitrex 3-15x50 scope on it and it will knock the center out of the paper target all day at 100yds using brown bear or surplus ammo and will shoot one ragged hole with Winchester soft point hunting ammo. It's just a fun gun to shoot