Thinking out aloud Joe, as I'm prone to do lately I'm thinking of using up old shot out, rusty or otherwise unserviceable barrels in this respect. So the value would be pretty well zilch. In much the same way that we'd use similar barrels for BFA. Start by cutting away the rear .906" breech end dia but you MUST protect the barrel to body surface.

A lathe with a long bed and a fixed roller head steady could support a barrel mounted muzzle end in the headstock chuck while a suitably and easily modified .5" dia and then a .7" dia drill bit could be drilled through in stages from a chuck mounted in the tailstock. Easily achieved as the .3" pilot is already there.

Likewise, bore into the breech end .9" and then .920. That is the 'old' barrel part finished. Time taken using friends large lathe 45 mts. Time to clean up swarf, cutting fluid and lathe, 1hr! But no doubt there WILL be a machine shop locally that could easily do this on a cash basis. After all, this is simply deep bore drilling a hole as opposed to deep bore fine finish boring

Regarding the locating slot on the underside of the barrel. It's true that some Canadianicon (or was it UKicon) barrels didn't have this slot. But that's because the barrel was located between the large upright ears of the Mk2 gun blast deflector. That's why they are there. It would be simple to machine off the female slot part if it wasn't needed. But don't forget that once the external parts of the barrel are machined then it's got to be stripped down for bead blasting and phosphating (and painting)