Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
There has been an amendment this month and black and silver plates can be put on a bike if it is declared manufactured before 1st January 1977, it is now on a rolling forward scheme like road tax.
Here is the new information from dvsa, i have a 72 350 four and a 78 Zed thou both will keep their yellow plates.https://www.mot-testing.service.gov.uk/documents/manuals/m1s06000301.htm
Bottom paragraph on the left, although it doesn't mention it's rolling. It wouldn't do; that date would change every year.