The stamped number on the headstock is the frame number (VIN), and the stamped number on the gearbox is the serial number for the gearbox.
I'm not sure where the engine number on the singles is stamped, but on the twins it's on the left side of the crankcase right under the left hand cylinder.
Enfield matched engines and gearboxes, and the number of the gearbox was stamped on the front of the right hand engine case (at least on the twins).
The UK REOC is very interested in acquiring numbers for existing bikes, whether running or not, for a database they're accumulating.
PM me and I'll give you the email address of the REOC president who you can send your pictures to. He'll send you a reply with the year of manufacture, and the date your bike left the factory.
He's been very helpful to me in identifying several old frames and twin-cylinder engines I have in my collection.