Rich,
I tried the setup in your third pic, but with a turned brass rod instead of a straight rod. I got the same side-to-side runout as when chucking it by the barrel band, but the up/down runout was now about .015. Seems like the bore is off center by maybe .007-.008 at the muzzle.
Anyway, the runout in your second picture is close to what I got in the very same location, so I guess these guns are not as precisely machined as I thought they were. That could make it iffy to get a new barrel centered, as you won't have any reliable index points. On the other hand: It won't be difficult to stay within Mauser's tolerances, a tape measure will probably do just fine...
