I have seen this set up before and they had the WB with 3/4" cranks in them versus the step crank. The 3/4" had the full 3/16" keyway and they used the double 12 tooth sprocket on both engines. Single chain going to the rear sprocket and the inner set of teeth connecting the two clutch drums. Lose one engine you still have drive to the rear sprocket. Just have to make sure both bushing are well lubed just incase this happens since under normal conditions the clutch drum only spins on the sleeve of the clutch at idle, once moving the shoes are locked to the drum and the clutch turns as one piece of steel and the bushing is non-functional which is why a needle bearing is not used because of cost and they cannot take heat above 250 degrees F. The crankshaft gets hotter than 250F.