The Monkees of Invention

Mike Nesmith and Frank Zappa switched places on 'The Monkees' - Episode 57 (out of 58) titled 'Monkees Blow Their Mind' which was filmed in April 1967, and first aired on 11 March 1968.
Bonus clip of Tim Buckley (aged 20) performing 'Song To The Siren' on 'The Monkees' after the jump... 



For ALL things Tim Buckley related go HERE. There are also lots of unreleased gigs etc to download that only require you to register.
(Highly recommended!) 
NB: Despite my personal opinion that Zappa was an enormous prick it would appear from the photograph at the Wiki link above that he was in fact only a small one...