First thing I would do is remove the bayonet and the lug. They can mess with the harmonics of the barrel. Then I'd find a stock that was the proper length and drop a recoil buffer into the reciever. That will make the gun fit you and reduce recoil. Next I'd have the crown redone and get a trigger job. I'd also probably end up removing the top handguard (allow better cooling) and probably replace the stock springs with Wolf springs.
Of course, you are also going to have to find a good scope mount.
Any chance the action can be trued, or at least be made uniform?
If I wanted to be really daring Id machine it to put a badger bolt knob on it, so its got an oversized cocking mechanism.
It probably wont work noticeably on an SKS, and its way out of price range (150$, and they might not even do it to an SKS) , but have the barrel fluted like they have on this page: http://www.pgwdti.com/ (done in canada too). Supposadly the corkscrew-like fluting makes the barrel more rigid and less sensitive to vibration but it dissipates heat better than any other fluting. If I can do it (and if theyed do it as a service to an AR), I think I'll send my AR uppers there for that fluting job.
Mabye a synthetic stock with a very small C&H Research mercury tube. Use the mercury not to absorb recoil, but compensate for the mass of the loose bolt flying back for shot consiistency. You dont need a full length model for this. Bedding the stocks would also help.
Re cutting and recrowning (use a step crown) of the barrel is essential.
Trigger work is also a must.
Potentially, put a stock, raw picatinny rail on the from of the stock (25$ off of brownells, dril the mounting holes and cut the length yourself and have the metal finished elsewhere/) and then get a bipod (harris is my personal favorite) and rail adapter to put on it.
If you can, try to re-work the barrel chambering. Re-ream for exactness.
Put a small bevel on the lower exterior side of the ejection port. This helps keep the brass going in slightly more uniform piles (this is really ment for bolt actions, where it keeps the brass in very exact short uniform piles).
Or you could leave it alone and accept it for what it is, a tough, fairly accurate, and very reliable rifle in the mid-caliber range. Take the money not spent and buy a Browning BAR in .270 or .30/06. I'm just messing with you, do what you want with your guns.