I know nothing more than what Gordon G. May's book "ROYAL ENFIELD_ BY MILES THE BEST" says.
A "Chief" is shown in the 1960 section and it had the deep full painted fenders with the Indian Head proudly placed on the front fender. The painted rear fender was also very deep with a rearward pointing flair at the bottom.
It did not have the Royal Enfield headlight nacelle and the instruments were mounted in a housing above the stand alone headlight.
The caption under the picture says, "Royal Enfield Indian Chiefs continue to be sold throughout 1960.
In this same 1960 section there is shown a "USA specification Constellation which has the chrome mud guards (fenders) that your photos show.
This Constellation does have the Royal Enfield headlight nacelle with the two parking light eyes on it but the text says it has " high handlebars and provision for a rev counter."
The British version was said to have a Black enamel frame & forks. The bodywork was polychromatic burgundy or peacock blue.
In the 1961 section there is a photo of a policeman sitting on a decked out Chief with the caption, "Matchless Indian sill advertise Royal Enfield Chiefs and Police Chiefs for sale in the USA in 1961.
This motorcycle has the Indian head on the wide painted front fender.
In 1961 there was a Royal Enfield "Interceptor S Sports USA Export Model. 692cc twin cylinder OHV. Bore and stroke 70 x 90 mm. Lightweight high compression pistons, balanced crankshaft, racing cams, balanced clutch, heavy duty gearbox. 52 BHP. Alternator electrics, Lucas K2F magneto ignition. Provision for rev counter. Armstrong rear dampers. Quickly detachable headlight, raised handlebars, 3 1/4 gallon sports fuel tank. Black enamel frame and forks. Finished in Chinese red & chrome."
The toolbox/side cover does not look like the one in your photos.
Hopefully someone else who knows more than I do will help you.