I think Arthur Bourne's first (pushrod) Square Four was one of the very few (10) with a DB engine prefix. Despatched on 4th Sept 1936, it had a variety of special features such as a spare set of H53 plugs in the tool box, a fabric clutch (instead of cork), a folding kickstart, and the new pattern tank knee grips. These last were the ones with ARIEL on them instead of the earlier John Bull type.
Clearly, "Torrens" liked to try out new developments but the folding kickstart was never fitted to many Ariels and I, for one, much prefer the soft springs and light action of a cork clutch.
"Torrens" wrote a book "The Motor Cyclists Workshop" which everyone on this Forum should read, given that it is obviously based around Ariels. The story goes that he changed the plugs on the first MK I he was given (maybe his Square Four No 3?) the evening before riding it to France. He stripped one of the threads, contacted the Ariel factory, who machined up their only other head for him and sent someone to his house to fit it. The person concerned was looking forward to working in the ideal workshop "Torrens" had described but on arrival found that it existed only in the author's imagination. He spent several hours fitting the replacement head in the cold and dark of the drive !
But I think "Torrens" would be amazed that, almost 50 years on from his retirement, Ariel owners still routinely ride their machines across Europe and back with very few problems - see the posts from Dave Owen.
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.