Yes Geo, quite correct, according to DVLA, "Vehicles made before 1 January 1973 may display traditional ’black and white’ number plates (for example, white, silver or grey characters on a black plate)", so I guess if you had some sort of build record rather than the reg doc you would be within your rights to run them.
Not sure about the 412 - love the early cars so 411 is the cut off for me.
Cheers, Roger
Further info on the number plates here:
https://www.gov.uk/government/upload...104_160914.pdf