Nice rack and nice set of clamps.
I've done a few racks like that myself. Stacking several on a bracket makes a lot more sense. The down side is that when you need that short or long one, its always the one against the wall. I can live with that petty annoyance considering the efficiency such a rack gives.
FORTUNATELY, I need to build a second rolling clamp rack. Built the first in NYW style, with one exception. I made the corners of the base rounded. Have a bunch of Columbian clamps bought at Big Lots, plus my Pony pipe clamps that need a better home, rather that stacked against the wall in the corner. I've heard it said that "You can never have too many clamps." Fast proving that theory wrong