Hi Ken, To me, a square chassis means one where the axles are perfectly parallel, and, I am not quite sure how spacers help with this ??
On the topic of spacers, while NSR/Slot-it/Scaleauto etc. do make reasonable spacers, companies like Koford, Cahosa, and, Slick 7, make 3/32 spacers for the higher end commercial type cars, where fit/finish/accuracy/consistency is far more critical…….their precision is considerably better, they are finished both sides, and they are no more expensive (in most cases less expensive) than the plastic car manufacturers products.
My personal favs., are from Slick 7, and they make them in widths from .005 thou. through 100thou.
The .005’s are to me the most useful, as you can use 2 between any rotating and non rotating surface to act as “thrust washers”, without taking up any meaningful lateral space.
Cheers
Chris Walker