GB, you amaze me with your interesting finds. The Daimler connection with BSA explains the curious application of the fluid flywheel on a big single to presumably give some smoothness to the transmission, in the same way as those ever reliable and effective (NOT) dual mass flywheels are supposed to on diesel cars. An early example of twist'n go, just like a far simpler Honda C50 Cub.
The Daimler Fluid Flywheel set up is more usually found with a Wilson Pre-Select Gearbox, more at home on a double decker bus to give smooth reliable take off with no clutch wear. No doubt expensive to produce, complex and a bit OTT for such a simple two wheeled application.
Hardly has the hallmark of market success.
Swarfy.