A couple of comments on your #s 5 and 6

"5.  Already own .303 button-style headspace gauge set.  GO gauge measures .0655" when SAAMI specs state .064"."
Have you checked this .0655 thickness with a mike? In a shop environment we only use the best electronic calipers if we have plus or minus .005 inches. Calipers are good for rough fast measurements, not precision.
"6.  Stripped NOS bolt (bolt #3) will not close on GO gauge the majority of the time unless I am carefull about the gauge's orientation.  Bolt will only close if GO gauge cut is properly oriented for extractor cut in breech.  Assembled bolt will close on GO gauge if gauge is properly oriented for extractor.  All other times, the bolt comes within just a few degrees of closing." Makes me think you have some slightly raised metal in the vicinity of the extractor cut in the barrel.  Have you checked the brass for this? Maybe marking this area of the brass will show it?
  If your gauge is really .0655, it is telling you something if the gauge must be perfectly aligned to close. I got a mammoth raised spot adjacent to the extractor groove on a barrel by forgetting to pull the bolt out before unscrewing the barrel, there maybe other abuses that could do that.
One other thing your new Forster gage will do is measure on the center of the barrel face. Krags seem to wear on the barrel face probably from dirty ammo. A flat gauge that is not centered will measure against the unworn barrel face unless perfectly centered.
On the attached photo you can see 2 distinct wear rings on the chamber end of the barrel. The outer is from the bolt face, the inner is from the case rims. I did file off the raised metal from the extractor accident, but you can see where you Forster gauge will measure.

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