Autoracks for GM plant

In regards to the GM plant in the Janesville, WI layout article, were bi-level or tri-level autoracks used? I’m modeling that area in the '60’s, and I didn’t know if trucks would fit in tri-level or bi-levels. And the period I’m modeling the autoracks were open, not enclosed, so I can’t hide whether it’s tri’s or bi’s!
Any help will be appreciated!