I believe you have an M28-30 with a SIG barrel, not an M24 carbine. It has the updated rear sight indicative of the 28-30. But it appears to be in good condition and is a valuable piece in its own right. I see no indication that it has been altered to .308 so I think whoever told you it was NATO was just confused. It should chamber 7.62x54R. Or technically 7.62x53R, the Finnish variation.
if you can get the measurements of the barrel that should tell us more. The 28-30 has a barrel of 27", while the M24 carbine has a barrel of just 24" or so.
NOTE: The barrel on the 28-30 is tightly bored at about .3085", so it is not an ideal rifle for shooting the .311" surplus ammo. However, the good news is you got ONE HECK OF A TRADE for a 10/22.
Probably not an ideal piece for a hunting rifle, though it can be handloaded and should give MOA accuracy with the right loads. It can bullseye deer. Or YOU CAN VERY EASILY trade this rifle, intact, for a scoped hunting rifle in the caliber of your choice. You did real good. Do not hack it, though, as you will hurt its value.
Here's a writeup on the M28-30. It was an integral weapon in the great Winter War of 1939, where the Civil Guard were often in the front lines against the Red Army.
http://www.mosinnagant.net/finland/MosinNagant-M2830rifle-introduction.asp
Value at recent completed GB auctions range from $382 to $450, but the SIG barrel is unusual for the 28-30 and you should look further into it before you sell or trade it. I suspect it may be a personal reserve M28 that a guardsman had upgraded to 28-30 status on his own dime. Only a few thousand of such rifles ever existed, and they were the tools of the finest marksmen. If you go to the collector's forum here they can nail it down for you:
http://forums.gunboards.com/forumdisplay.php?3-The-Collector-s-Forum-Mosin-Nagant-HQ
If you explain your situation I also have no doubt you can trade it off for a nice scoped hunting rifle without problem. That's a collector's item you have. A true piece of military history. A rifle of white death as the soviets called them.
Check out this ad, touting the "new barrel of domestic steel." Your barrel is SIG steel, which is absolute top-notch obviously. The fact that it's on there is of real interest, but I don't know enough to say what impact it would have on the price. Ask the forum gurus on the gunboards, they'll know.