Hi Martyn,
Nice Welbike, and you did well getting rid of the mod's!
Some notes on the markings, the little caution transfers on the tanks were never white only, they had a black background, all the original paint Welbikes I owned and still own, have them, one day I'll reproduce them!
Then the Census number, on the 3rd contract, all the WB's had the last two digits from the frame number as the C number, so yours should end on a 6 too.
Too bad the tanks were overpainted, otherwise you might have known the complete framenumber.
Incidently one of my WB's frame numbers is 3059, and that has C5153859 on the tank (original paint and the numbers are actually transfers, another thing to make!)
Your C number is something like this:C51538?6
Also your frame number is a little high, when comparing to others in my database, mine is 3292, they certainly never match, but vary from 50 to 300 digits.
The War Office tried hard to get all manufacturers to end the Census numbers last two digits to match with the last two frame numbers, and to match engine and frame numbers, but Excelsior only partly complied with that! but that was certainly not the only manufacturer to do so.
Hope this helps,
Cheers,
Lex Schmidt, Holland
ps, Strange to see myself as an aftar all the time!