10 mm is only .39 inches... at the bellhole... I don't think that is such a big deal at all. Lots of old K's have bell hole issues, and if you mount them right and don't tighten down the wingnut too much, they won't get any worse.
The rarity of the old stamp, the super thin weight, great sound (btw your other soundfile: the one I heard on cymbalholics was a much better representation)... i still think 2000 is a pretty reasonable price. Someone out there will want it that badly.
As soon as I win the lotto, I'll send you a PM!