There is a list of impressed serial numbers at the back of O&M's book. But no way of working them out I'm afraid.
I have been told that the serial number was simply stamped on the crankcase (not painted on the bike) I know a few have come to light and I have actually just done some work on such an AJS for a friend. Ron
No Ron sadly you cannot, but you can at least pick a number from an appropriate block.
Just think how silly you would look if you put a number from a captured Tiger tank on a 1940 Autocycle which had previously been owned by a district Nurse!
Spoilsport
OK Rob how about this line of civy painted impressed AJ's. Clearly they have painted the C number on the number plate. (Taken from Gavin Birch's book) Ron