Those barrels can look pretty bad. Get a good 30 cal bore brush and some Hoppe's, and spend some serious time scrubbing the bore before you give up on it. It will never shine, but it might clean up.
If it doesn't clean up;
Barrel replacement on that rifle is a fairly involved process, and would be expensive, and that's assuming you could find a decent correct barrel for it. It's definitely not worth as much as a good shooting M39, but it's still an M39, worth a few bucks to a collector, maybe. If you really want a good M39 shooter, pony up the bucks for one with a good barrel. They're still fairly common.
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