He also got to sit in on Zappa auditioning bass players in his LA-based rehearsal space. 

Park recollects: ‘Frank was sat on this high stool, while I was sitting in an armchair. The bassists had to perform the bass line from Frank’s songs, which is difficult enough! Most got about two bars in before Frank would stop them and tell them they’d got it wrong. They got a few shots, but it wasn’t the easiest environment to rehearse.’ 

Maybe Frank wore the Radio Clyde shirt because they played his music. If so, they were part of the few and the brave among the many who took their advertisers and themselves way too seriously.