Most bikes used the frame number as the VIN, Older Japanese bikes did not have matching engine and frame numbers and used the frame number. The MK3 Commando ( Like LAB shows) had a small stamped in frame number along with the red tag number and it was confusing in the USA the bikes could be titled with number for some reason .
(My MK3 uses the red tag /engine number, but I had a MK3 that used the frame number)
Whatever the bike was once registered with or titled would be my choice if it were in the USA.
You can use the March date 1972 . As that is as good a number as any and fits the engine VIN.
If it was a MK3 frame I would use a year of 3 /1974 as that is when the frame was used/ made.
I would look at how the OEM tags were stamped and what font and copy what an OEM tag looks like.
If you have a MK3 frame at least you have real factory numbers, and that makes it legit, IF the bike was never reported being stolen. But that is a whole other can of worms.
At one time I think it was Andover Norton? that would stamp a tag for you if you brought a tag from them and proved ownership of the bike. Check with Andover.
