Who said they were road bikes? Can replicas only be built from road bikes?
In any case they were "fully equipped road going versions, which did not make it into production" So the hang up for you must be production. Dan was particularly interested in replicating this bike because it did not go into production and also because none of the originals remain today. It represented more of a challenge to him than just measuring and copying a currently existing motorcycle. I recall that he spent about a year on drawings, which are quite beautiful. Once he had the drawings complete, the bike was already built in his mind, and a sharp mind it is.
The top end looks identical to the schematic from 1935, in fact that is what the engine is built from.
"1935, at the Olympia Show, the Bert Collier designed air-cooled sohc AJS 50° V4 was first displayed. It was a fully equipped road going version, which did not make it into production. This first version used a common crankcase with four individual cast iron cylinders and separate alloy heads, with exposed hairpin valve springs, and a 180° crankshaft with forked conrods. There was a central carburettor for each pair of cylinders, and fore and aft exhausts. The single overhead camshafts were chain driven. It had chain primary drive in an oil bath primary chain-case, and a wet clutch. It was stated by AJS at the time that there would be the option of replacing the forward mounted chain driven dynamo with a supercharger. The AJS used a rigid frame with girder forks."