OK I am not a mehanic, and this does sound complicated, but all the same... pretty simple...
"..the engines sit end-to-end with both of the gearbox output sprockets lying along the centre line of the car.
The engines are sat in an upright position to optimise the operation of the oiling system and to make a compact fitment. A bespoke transfer box is used to combine the drive of the two engines. This sits between the two engines and connects to the two drive shafts which transmit the power to the wheels...."