Well you can forget getting a replacement barrel for the No 4 to the military spec but you can get something like a Douglas barrel and had it put on and kind of sporterize it.
I have rebarreled several with a custom made reamer that does not allow the big expansions the military chamber allow. Big chambers reduce brass life tremendously.
They are not that hard to rebarrel but I can understand why a lot of gunsmiths won't mess with them as the barrels can be extremely hard to remove as they are very tight.
The buttstock can be tightened up with Marinetex.
With a new barrel it would be headspaced to the bolt head you have.
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