Marty
I have not noticed an issue with tire rub with the original wheels and tires. It could be possible that the Slot.it tires and wheels are wider and might rub. The chassis to body spacing can be adjusted with the outer front grub screws, pushing the body upward from the chassis. I would like to check further to investigate this, but my initial feeling is that spacers would be allowed, but unnecessary, on the front posts.
The coupe track can be widened 2mm from the spyder track. As the coupe is ever so slightly slower than the spyder, this could be an equalizer. If it gains too much advantage, the maximum track width could be specified but my initial inclination is not to spec it. I will test this also.