You mean the Brazilian and the Chilean?

My advice is not to touch these. They are for collectors/shooters of ex-military firearms. It would be a shame to modify these.

The cost for an ex-mil action and new barrel would probably be similar to the price of these anyway. The ex-mil barrels are stepped and would need work to streamline the profile. Realistically if you buy a beat up Mauser you are buying it for the action only. I'd stick with a 98 action.

On the other hand there is a 96 action (ad says M38 but this is actually a 96 action) that has been customised to some extent, has a scope and is 7mm-08 and is only $600. That looks like a good deal and you could rechamber to 7x57 without too much drama maybe? Even if you change the stock, mounts and scope, you're paying $600 for a modified action and barrel with the size hole you want.