ORIGINAL: Mr Cox
Yes, they most likely have common parts with car and boat engines, much like the OS 15CV has. The HPI one is true ABC with a strong aluminium conrod, while the KB one is an ABN construction with a brass/bronze conrod...
From a distance one can barely tell them a part (carbs are identical too);
The HPI engine is most likely made by Toki. I have an HPI .15 car engine that came to me with a blown out rear bearing.... The engine hadn't even run yet. ABN cylinder/piston, single needle car carb, bronze conrod. Stamped "Made in Japan" as the above HPI engine. I have mine over at a buddy's shop to see if he could make a prop drive for it or find a way to put a prop on it. Not strong engines, but they run. I know little about the K&B version though.
At first I thought it might have been made by OS, but I looked further and found it to be most likely a Toki.