Rob, my opinion was based upon the fact that it's a lot easier to change the tang than the barrel, especially without leaving tracks on the barrel breech area. A fairly sure indicator would be to closely examine the juncture of the tang with the bottom of the receiver, comparing the polishing lines and mating surfaces where the two meet each other at the trigger area. These two parts were always polished while attached to each other, and the junction should be perfectly even and smooth with no rounding or sharp ledges/steps or other indication of separate polishing.
A separate new barrel could be made in literally any caliber by simply furnishing a new extractor of the appropriate size, to be swapped out at the same time as the barrel. The only limitation would be the size of the barrel shank. The original forearm could be used if the proper size, or a new forearm made for the new barrel if needed.
I'll look forward to receiving your rifle, it sounds interesting.
Regards, Joe
