One I never expected to find. Glenn Cornick with a Thunderbird II in 1969. Very brief clips around 1:50-1:60 or so.
That clip is a bitsa mashup of footage from 1976 and a later lineup and period of Tull. The 1976 clips come from the show 'Supersonic', and a more complete copy is here;
This is the
Too Old to Rock 'n' Roll: Too Young to Die! incarnation of the band, so the bassist will be John Glascock. He used a P bass, and then moved on to a Stingray, so I don't know where the T-bird II came from, unless the band repo'd it from Glenn when he left? In the Isle of Wight footage, Glenn's bass has a black pickguard with a USA/CND flag on the pickguard. In the Supersonic clip the bass has a white pickguard, so it might not be Glenn's bass at all!
I'm not sure if this clip has been posted before, but it is quite good. In the interests of science a bloke plays 3 different Greco T-birds from the '80s. Does that make it a three bird roast? A Turducken?