I found a like new Sako barrel, which I though about putting in a "non"-barreld Mauser I have lying around.

I am wondering if this could fit? Its an Varmint barrel, so there is perhaps some metal left to cut of the threads, and install in the Mauser?

For a large thread mauser you need 1.1 inches OD foe a new thread. For small thread, you need .980, plus at least a small shoulder. So, measure it and tell me the OD. And, you will need .625 long for the threaded shank.

Some "SAKO" -named barrels were made for High Power -models. These ones have normal Mauser LR threath because those SAKOs used to have ordinary FN civil-Mauser action.