Location: 3 miles NW of Brownells retail store and they keep me broke!
I once built a 22-250 on a 98 small ring mauser. It took installing a block into the magazine and a shorter follower and spring. I bought the follower and spring from Numrich. They were initially for a 243 on a MKX action.
I would just do the 308 and load it light. I would also try it and see how it feeds before I altered anything with the follower or spring. There is a good chance that you will be fine.
If you can find a shot out Remington M700 barrel for cheap at your local gun shop, you can avoid the trouble of drilling a hole in your test stub. The M700 barrel, and others, has a large enough shank to turn down to .980 IIRC small ring Mauser diameter.