Paul Colbert interviews Zappa in Zappa: Speak Out, Musicians Only, January 26, 1980. Another fine article from afka.net.
This one's about Joe's Garage -- yes, it is a series of discrete songs with a narration written in after the fact -- and it gets into a number of Zappa's usual favorite subjects, like the rotating band membership and his love of new technology.
Oh, and it's not just the narration that was added to disconnected songs on Joe's Garage -- the solos were, too.
Now here is an example of being different. The solos in JOE'S GARAGE had very little to do with the backing tracks. They were all recorded on the road TO OTHER SONGS.
"I came back with a stereo Nagra tape of just guitar solos and thought of songs where they could go. You try to find something that's in the same key but the time signature could be different. In "Packard Goose", the backing is in 4/4 and the solo was played in 15/16 in a totally different tempo. It was from the last show in Zurich during a song called "Easy Meat". The solo in "Keep It Greasy" – the rhythm background I think is in 21/16 and the guitar is in 11/4. The beats come together about once a month ..?