I believe Zappa to have been straight drug-wise, apart from the fags of course. There is a story of him being handed a lump of dope by a fan at one of the 60's London concerts and not knowing what it was.

Anyone ever read Ben Watson's book Frank Zappa: The Negative Dialectics of Poodle-play ? Highly recommended.

Mention of Jimmy Carl Black reminds that I once sang Lonesome Cowboy Burt at a folk club many years ago. Here's Jimmy's masterful rendition from 200 Motels - featuring Zappa himself (and Aynsley Dunbar) on drums; George Duke on trombone; Flo & Eddie - sublime harmonies...

http://www.youtube.com/watch?v=-eN-ScHMdC0