That's strange.
One would think that if the barreled receiver fit into a synthetic USGI stock, then the same barreled receiver would fit into a USGI wood stock as well.
Now, is it possible that the wood stocks you tried absorbed moisture at some point and swelled up, thus causing the receiver legs to bind? Have you tried a couple of different wood stocks?
You may need to measure the dimension of the receiver legs to see how out of spec they are and make a decision as to whether it's worth having them ground down evenly to spec, or just finding a good receiver and replacing the one you have. I just consulted The U.S. .30 Caliber Service Rifles (A Shop Manual Volumes I & II) by Jerry Kuhnhausen, and I don't see those dimensions mentioned in the text or illustrations. Maybe I'm overlooking them.
Maybe just keep it in the USGI synthetic stock you have and call it good. How does it shoot? Does it pass a full function check?
Is the rifle made up of USGI parts, or are the parts Chinese? If the parts are USGI, it may be worthwhile to replace the receiver with one that's forged and within specifications for geometry, materials, and hardness. I have three LRB receivers and they are awesome. I've heard very good things about JRA and Bula Defense too (next build will be with a Bula Defense).