Ian, the KDC on the base of the cylinder may mean Komatsu Dresser Company, which was a joint venture between Komatsu and Dresser, intended to supply very large mining haulers. If so, I don't have any idea why it would be on this product.
I take it the rectangular port is the intake. It is not especially low on the cylinder, and has a definite cut-off on the lower side, so it looks like a piston-controlled port to me. Does it have a reed valve in between the carburetor and that port? If not - that is, if you can see straight through from the air intake side of the carburetor to the cylinder when the throttle and port both open - it is a port controlled, crankcase induction 2 stroke like a Victa, Villiers, etc. (it just runs better than they do).
It appears B&S only stopped using the engine because the strong Yen made it too expensive - I haven't seen any suggestion that they were unhappy with the engine itself.
