I'm still not totally convinced that the chassis rolls down the tilted test track as smoothly with coupling rods as without, but it's close. I still need to attach the motor and see how it runs. Luckily the wheels are just held in the muffs by friction so are still adjustable. I haven't decided yet whether to glue them or not, but if I opt for glueing I want to check more carefully with a back-to-back gauge first (which I need to obtain...).