Little bit of progress to report:
I managed to acquire a brand new set of loading dies for this cartridge, made(?) by the Vanettens of Bullzi Projectiles. Apparently the local Darwin pistol-smith I mentioned earlier (Graham B__) commissioned a bunch of them, and still had one set left unsold!
I should buy a lotto ticket...
He confirmed the barrel on my newly-acquired Colt is a King's (USA), although it is unmarked but for the ".38 JWH" caliber stamp. Not sure how King's cut their barrels but they were imported already chambered apparently.
Meanwhile, B__ had convinced Clymer to make him a reamer by altering the shoulder angle on a .38 Casull by half a degree and stamping it ".38 FJH"...

He then set about rechambering Aussie-made Lissner barrels for interested parties.

While my gun is nice and tight, it seems the barrel will need a bit of adjustment to improve the fit before I start volume shooting.
Now waiting for a rainy day to run my .45 cases through B__'s form dies (all four of them, plus the FLS die to adjust headspace to ~zero in my barrel.
More beers...(sigh)

Never ceases to amaze me how much history can be uncovered by heading off down these crazy historical rabbit-holes!