Price the cost of a custom gun before you get too deep into this. It is easy to spend more than $1500 and end up with a rifle with a resale value less than $500.00
I get to meet interesting people at Regionals, and between relays got to talk to an individual who works for a failure analysis firm, specifically one that is contracted to investigate product liability cases. Since we were all active in the match, had a limited amount of time to pump the individual for information.
He had been contracted to investigate an incident involving a German made, Turkish owned, GEW 1888. The rifle was a rare one, because it had the original 0.318" barrel. When the Germans changed the bullet diameter of their 8 mm round to 0.323, they went through their inventory and aggressively removed the barrels from the old 0.318" barrels, and put on new barrels. The buyer of the GEW 1888 of course had no idea of any of this, and did not slug the barrel (who would?) fired 8mm Mauser ammunition, which had the 0.323 bullet, and the lugs sheared. The bolt went through the shooter's jaw, and through his shoulder. The shooter was of course suing, because the rifle had been sold as being chambered in 8mm Mauser.
The point of this is, those small ring Mausers, and many older Mausers, will blow out their bolts as they don't have safety lugs. That, plus the uncertainty of the metallurgy of the things, means, you are better off buying a new rifle, chambered in the cartridge of your choice, for around $400. New rifles will have better gas protection, will be several times stronger, just due to improved materials. And of course, cost less.
If you really have to have that small ring rebarreled, have the action re heat treated, that will be about $300 and die penetrate tested for cracks. Do the cracks first. Re heat treatment should re case hard the surface and hopefully do something on latent cracks inside the action. It won't remove the residual elements that make the steel weaker than modern plan carbon steels. That crap stays in there. Incidentally, the cheapest Chinese nuts and bolts you buy in the hardware store, are made of cleaner steels than those historic actions.