The 760 mags are all the same box. The difference is the followers and the spacer blocks used in short action calibers. If you look at the photos above you can see the spacer blocks. If you can find followers for te 35 Rem you can use any of the short action cartridge mags.
The mag boxes are the same but there are some dimensional differences between the feed rails on top of the 308 and 35R boxes. The 308 boxes will not fit into the 35Rem rifle without forcing it. While I have not tried it yet, I think that some tweaking on the rails on the 308 box may allow it to fit.
Both the 35Rem mags in the pic will properly feed ammo into the rifle so the different follower doesn't seem to be a problem.
