The Wardill.

[R]

And the Norton Wulf was a 500cc parallel twin, stepped piston design, somewhat like the Dunelt as you say.

[wildun]

Also the Commer TS3 /TS4 and the Foden all very successful (and fuel efficient) trucks, but very noisy because of the Roots superchargers.

The Wardill engine, although a supercharged two stroke was unique in its design and did not employ popprt exhayst valves in the head,  (the Commer did not either ) - too bad the Wardill concept didn't come to fruition.