Seems easy enough to plop an open cab on an AA? Could have been at the the dealer or at home. CCPU and open cab have the same footprint from cowl to back, no?
Perhaps the term "roadster" implies a folding top, and no side glass, as opposed to "open cab", or fixed soft top and no side glass. I helped restore a "roadster pickup" last year and am working on one right now and it seems like the "76" or "82" would have been used to designate either an A or AA.
I'm not the oldest Model A guy around but I've never seen an open cab on an AA. Certainly seems like a good idea for hot climates and surprising it didn't happen more but maybe hauling a loaded big truck with nothing over your head but some cloth isn't the smartest? This truck has a sturdy headache rack built on the flatbed so it probably occurred to the guy who used it. He definitely means business with that horn going straight through the the dash! -Chris, also in Boulder.
-side note- Neil, I just moved to your side of town. Sold my CCPU recently but I cruise by your place in my T all the time. Hopefully we'll see you around!