How much distance is the top level above the lower level?
It is actually 30" top of benchwork to top of benchwork. Subtract the width of the 1x4 upper deck framing and that leaves 26 1/2" of usable space.
The lower level is 42" off the floor and the upper is 72". I have also raised the floor 12" in most of the aisles, so the upper is at 60" relative.