DVLA have date of registration as 1987 so at a guess it was put together and re-registered for the road then. (Roughly matches with Roger's first record, and back then they were a lot more flexible about numbers than they are now - speaking from experience!)
My reference for registration numbers also has XVT Stoke-on-Trent from Nov 1955, so getting closer to the date and place the bike was originally supplied to.
https://www.oldclassiccar.co.uk/registrations/vt.htm
According to the Kithead Trust website there are still records for Stoke-on-Trent registrations up to 1958 so maybe someone tracked down the original registration!
SG