I wasn't at Air Fete 80 at Mildenhall and I didn't get a glimpse of a section of black fuselage through a briefly opened hangar side door... I haven't just looked at my old mil spotter's log (can't bear to throw 'em out, after nearly 30 years, God only knows why) and it wasn't 68-10339.
I did however see and hear one take off from Patrick AFB - the log I didn't look at tells me it was 68-10329, the history of which ORAC has kindly detailed above. I recall the climb as quite steep and I was surprised by the noise. Mind you, I think I had seen the TR-1 flying at a show or two by then. The departure was just before the the first post-Challenger Shuttle Launch so possibly connected?