I know of at least 6 very close to me that are pretty much restored / customized, and a seventh that was in process before it got wrecked - it's back to long-term project again. Half of them are daily drivers, half are more of toys but nice nonetheless.
How about getting in touch with vendors? Adding up the total number of customers of customers should give a rough estimate (although definitely on the high side since I bet most of us have bought parts from several vendors). Think about it; anyone who's restoring or has restored / customized one of these trucks has to be a customer at at least one vendor. I highly doubt many of these guy's sales go to people with no intention of making a project out of their truck.
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Project 1970 - soon to be seen at
http://milhouse.treylis.org:81/