...which is why the original three wheeler used several different engines over time....
HFS used to play off one engine maker against another to get a lower price, and price was very much the issue with vintage three wheelers. That and which engine the customer chose dictated what was fitted. At times, there would have been more than five listed engines. (JAP supplied three at the same time, A/C sidevalve, W/C sidevalve and W/C OHV).
The prototype had a Peugeot engine, JAPs are probably the most numerous, with Matchless, Blackburn, MAG, and Anzanis also fitted. There probably were others, but that's the ones I recall. Anzani went bust - partly because of Morgans price policy and the valves made of poor quality steel.