To make it feed as Paul Mauser designed, you'll need to replace the mag box and follower with one designed around whatever caliber you choose to use, as well as some work to the feed rails and ramp. Having personally tried to do a few cheapy conversions without properly designed bottom metal, I highly recomend avoiding that tact.
The best option is to stick with the factory bottom metal, and use a round based off the X57 case, so a 7X57, 30X57 wildcat or stick with the 8X57. The rounds have excellent performance and just as importantly they'll feed nice and slick just the way master Mauser designed them to.
