I've made one fake truck - with the wrong colors - and it runs very smoothly, a bit smoother than the passenger train, because this loco is fair bit heavier. From a distance the fake trucks look fine, as it is quite dark under the loco and the brick work hides where the wheels hit the tracks - the only time where the illusion fails is around corners, which is where the running for different truck models fails.
Man, I'm starting to dislike LEGO corner tracks - but the flip side is the gauge of the trains is so big you need a lot of space to play with layouts, so I can see why they tried to keep the corners tight.
I have some Steam drivers on order zephyr, so I am going to take you advice and muck around with a steam train chassis first, before I try and build the whole thing. One thing this diesel loco has taught me, with LEGO trains, is to start from the wheel design, then work out what kind of motor you need, then model the train.