Clayton - welcome to the forum.
I'm not familiar with the 1930s/early '40s bikes but I've not seen engine numbers without letter prefixes or just 'X' as a prefix for a rigid single frame number.
Are you able to have a good look at the drive-side crankcase between the front engine plates to see what letters/numbers (if any) are stamped there? (Usually between the lugs and going 'round' the case, not across it.)
Also some pics of the whole bike (each side) and the numbers on the gearbox would be useful to the folks here who are more knowledgeable!
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)