Now that I've re-found this thread (& scoffed down some lunch) - and the question has been answered. (Yes, power)
I don't know if any of the earlier decent classics were capable?? The Vincent? The Suzuki T500 Titan was around at the same time as the mach III and there were some Suzuki and Yamaha 2-stroke dirt bikes around at that time that were probably capable of powerstands to.
You might be interested in these links I found while I was doing a bit of a search... (no ref's to wheelstands but still interesting).
http://www.suzukicycles.org/1960-1969/1969a.shtml
http://www.yamaha-motor-europe.com/c..._1955_1969.jsp
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