Regardless of any of the drawings, I can say with a degree of certainty, based on nothing more than my experience, that whoever makes replacement barrels, there will NEVER be a barrel that will interchange or be acceptable throughout the No4 body range. Because while all the new replacement barrels will be made to a plus/minus toleranced drawing, so they will be fitted to plus/minus toleranced bodies. That means you will get the variables that I mentioned in an earlier thread.
But, if I was given the task of formulating the production engineering, I'd start by (sorry chaps........) saying 'forget an extended tenon or any means whereby the owner or gunsmith can re-set his own CHS'. NEVER, never, ever allow this because once you do, you'll have a new barrel fitted and CHS'd to a totally clapped out body which in real terms would warrant a No10 bolthead! When we know that after a No3 bolthead, it indicates a worn out body. I appreciate that another nation made a No4 bolthead, but the design engineers and post war trials suggest otherwise. But just think about it......... why didn't they just go up to No10 - or 15?
Then I'd say that the breech end can remain as-is BUT, the rifle will be breeched up using the extractor slot as the visual guide and the nocks form square against the backsight axis pin as the breeching up torque limit. Spacers as per the late No4's/ L39/42.
The muzzle end is machined down to accept the foresight block band and bayonet lugs that take the form of a simply machined collar that is sweated onto the barrel and squared on a surface plate.
There it is. A barrel that will fit to any body, will detect a worn-out body, will correctly align, correctly torque up and with foresights/bayonet lugs that will align. The GOOD thing about this method is that only the serious or skilled gunsmith will be capable of fitting it. Those who are politely described as 'enthusiastic amateurs' won't manage it - hopefully
Just my views thinking out aloud. But be warned, that while there will be barrels made to drawings, there are also bodies made to drawings too. That's why we had a big rack of barrels.