Thank you for the comprehensive and informative reply.
I have been collecting license plates for about 50 years, and have learned quite a bit about the details, but just now learned something new, so it is appreciated that you took the time to compose such a great reply.
I recently reregistered my 72 240Z, using the original license plate as “year of manufacture”. It is now permanently registered, although use is limited to test drives after maintenance or repairs, parades, travel to and from shows, or for pleasure.
 
 

You are most welcome chap - glad the musings of a madman had some value.

The original Q plate:

As I was reading through this thread, I was thinking the very same thing that Alan ultimately said, This is a 'Body in White.' I have never heard of Nissan or Datsun supplying a body in white to anyone. Porsche does, but if you ask about a BIW they will tell you NLA... 

It follows, as Alan said, this adds credence to the BSR connection because you'd have to have some serious stones to get Nissan to supply a body in white. If this was stateside, I'd definitely consider it at that price. In fact, it might be on the low side. Never mind the BSR connection, it's a body in freakin' white! You can't do the paint and body on your project to bring it to this starting condition for that price!