For series A and Pre A bikes contact the Machine Registrar & Researcher
For series B, C & D here is where the important numbers can be found.
Engine number is located on the LH side crankcase. The crankcases may have HRD cast into them, or Vincent or may be blank, ie no manufacturer name.
Crankcase mating number 1000cc (twins). This is located on each crankcase half between the cylinder barrels.
Crankcase mating number 500cc (singles). This is located on each crankcase half behind the cylinder barrel on most, but not all machines.
Upper frame member (UFM) number. Located on the headstock and this is the frame number used for UK DVLA registration applications.
RFM (rear frame member) number. Located on the left side rear casting just in front of the rear wheel spindle. This frame number is not used for DVLA registrations but is still important when mentioning matching numbers bikes.