The british mauve engine would probably have been an Apex. These were unusual because the engine actually leaned backwards, with the exhaust coming out of what would have been the 'front' of the engine had it not been tipped back.
The thinking behind this was that in a usual rear exhaust engine, the thrust side of the piston is the hot exhaust side. By putting the exhaust on the front, the thrust side of the piston is the cooler other side. This makes the motor less prone to seizure.
If you don't understand the concept of thrust side of the piston, image which way the rod points and which side of the cylinder the piston is being pushed into on its power stroke.
The other interesting design feature was that the reed valve could be removed so that a cartridge rotary valve (of really weird design) driven by a belt could be fitted.
Don't know why they never took off.
The forward facing one ian is talking about might be a Sonik
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