I worry that 2 motors will mean slightly less weight. Ever since the Rivarossi Y6 these N scale steam locos have been a bit prone to wheel slipping rather than pulling. Having 2 independent motors will mean the 2 engine unit can get in and out of synchronisation will look very prototypical. They'll need 2 DCC sound cards to keep the sound matching the driving wheels. I would have just gone for 1 motor, more weight and had slightly varied pitch on the worm gears so that engine units and therefore the connecting rods appeared to run independently.