I'm with you here, while I am no engineer I would think that to lessen the stresses on the coupler and both engines in general (ideally they need the same power output I would assume) or one will be taking from the other and that's not the intent of this build I would think. The turbo engine would be overpowering the first engine, straining the two and at that point the second engine will be working harder to make up for the differences?