Definitely not a one-note wonder, by the way: In addition to this instrument, he also built a carillon of airhorns mounted on an old Citroen truck, and busked as an acrobat and comic performer.
Those cassettes for sale at his stand (note they were still in francs!) included one called L’Organiste Barbare, or The Barbarian Organist, with compositions of his own as well as selections from composers as disparate as Dave Brubeck and Waldteufel.
I’ve wondered for a long time if he’s still out there; I’ve never run into him on other trips to Paris.