RE: Mauser 98K
If the headspace is the only issue, and it' s only off just a wee bit, you could get it reamed to 244 Remington/6mm Remington (same thing) as it is just .178 longer than the .243. Granted, the ammo will be harder to find, but if you handload anyway it will make little difference.
If your chamber is off by more than that you may want to try a reaming of something bigger like the 243 Rockchucker. It is based on the 257 Roberts case and is a bit superior to the .243 Winchester.
If you don' t care for the .243 bore at all, then good luck with your choice of new barrels.