Just a note of possible interest about 7mm Rolling Blocks: They may show excessive headspace, regardless of the condition of the barrel. The reason is NOT due to excessive loads, etc. When American ammo makers "brought" the 7x57mm cartridge over here, somehow the specs for headspace got shortened over the specs in Europe. The result is if you shoot U.S. made 7x57 cartridges in most (maybe not all) 7mm Rollers, the cases will stretch. Not enough to create a dangerous condition with head separations, etc., but if you go to reload the brass, and resize it back to U.S. standard, pretty soon you will stretch the brass. Best thing is to back the sizer die out until you can just chamber the case, or (2) neck size only, or (3) form the cases from something longer, such as 8x57 or .30-06, etc. While the 7mm Roller is a stronger action, I wouldn't heat the rounds up all that much, and watch out for the case heads to bend slightly due to the breech block rotating back a bit, regardless of how tight the action might be.
As to what to rebarrel it to, it depends on what you want to do to it. If you want a medium bore, you might consider .30-40 Krag, .38-55, .40-65 WCF, or .45-70.