I never thought of doing that
As I said before, to do this legally the V5 and reg number are of no use without the original frame (or a NEW frame to same spec from the manufacturer.... which obviously you cannot get) and at least 2 original major components i.e engine, gearbox, wheels (both), forks.
see this link https://www.gov.uk/vehicle-registration/rebuilt-vehicles
Now there is no way of telling if the forks / wheels (and maybe gearbox) are definitely original to the reg number so as long as they are the correct year you may be OK.
BUT with a classic bike you still need the original frame NOT just a bit of it with a frame number on it.
So...the only way that the V5 on sale is of any use is if you use it to change the identity (frame number) of the same model and same(ish) year bike to match this V5. And why would you do this...unless the bike you have was stolen?