It's more than likely that the work was done by a dealer or gunsmith, rather than the factory.
Colt had barrels and cylinders readily available - they wouldn't've been over-stamping.
In the 1960's, these, and many other Brit revolvers came to these shores via 'Ye Olde Hunter', 'Walter Craig', and Sam Cummings - to name but a few.
They were often re-chambered to the more 'compatible' .45ACP, because of the profusion of cheap ammunition.
Many of the little Enfield .38s had their barrels shortened to the non-existent' 'Commando' length, while untold Victory Models were re-chambered to .38 Special.
Often, the work was done locally - though Parker-Hale did do a lot of contract re-chambering before shipment.
Colt and S&W weren't in the business of refurbishment - they were trying to sell new commercial weapons - and though it's not unusual to see ex-GI parts on guns produced in the late '40's, they were well-polished.
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