Royal Enfield on eBay worth more than seller knew?

A Royal Enfield with a Japanese twin-cylinder motor.

A Royal Enfield powered by a Yamaha XS650 twin cylinder motor would be an interesting proposition. But never mind the motor; what if the Royal Enfield itself was old enough and rare enough to be interesting?

This is the case with a 1958 Royal Enfield Meteor offered on eBay in New Castle, Penn. The seller only learned after listing it that the motorcycle "is actually older than I believed. The brass tag T7 would have been a very much earlier chassis, possibly a very rare bird as well. If you have any serious interest, feel free to call me. Until then I will be doing some research."

You can call the seller at 724-971-6203 but, for the moment, he is pulling his ad off eBay.

The change of heart apparently came when the seller was contacted by Graham Scarth of the Royal Enfield Owners Club (REOC) in the UK. Graham has a sharp eye for Royal Enfields that may have been built in Redditch, England and either show up (or are missing) on the Royal Enfield factory ledgers the club holds.

When the ad appeared on eBay, initially as a 1963 as I remember, Graham wrote the seller this note:

Tag on rear fender holds clues to motorcycle's origin.

"This Royal Enfield chassis is older than you think. T7/1561 was a 700cc Meteor dispatched from Redditch in March, 1954 to a French dealership called Psalty in Paris. I am intrigued by the brass identity plate. I would be most grateful if you could send me a higher resolution digital photo of this plate for publication in our Club magazine please."

This Royal Enfield may have an interesting history on its own but I would also like to know how it came to possess a Yamaha motor.

Anyway you look at it, it is an intriguing motorcycle.
Rear brake and gearshift are both on left!