Unkn

Question for those in the know.
Mate has done some work on a small truck built in the 1950s. It has a flat 6 horizontally opposed engine with a supercharger. All alloy gearbox. No idea what it is but wondering if anyone here might know?

Could be a Commer 'Knocker'...2 stroke diesel, 3 cylinder with 6 pistons. More info needed.