There might be a circulation issue with the k but with 1 cillinder and head it could work. I expect there to be impeller my self but I think the subject is worthy of debate JJH
For thermo siphon to work you need a good "head" hight of liquid and a uncomplicated path both flow and return with as few bends as possible to reduce restience to flow. You give a f as an example but the part that needs cooling in the engine is quite high and to promote a good circulation the heat exchanger(rad) would have to be too high up in the frame. JJH