Reed valve = not pre-70 legal.
The ol' DT1 is reasonable pre-70 race bike, but is pretty seriously outclassed as a pre-75 bike.
So if you've got one, then the 'sensible' thing to do, is make it a pre-70 bike.
You don't need to have a square swing-arm on a DT1 to make it pre-70 legal anymore, FWIW.