It's the vamp that's around 2:14ish to 4:20ish on "Pound for a Brown Solos (1978)" from You Can't Do That on Stage Anymore, Vol. 4, which was taken from the October 27, 1978 late show.
I recently heard it again on this version of "King Kong" from the March 26, 1979 show, from about 1:30:57ish to 1:32:40ish (insane solo from Frank to finish this version off, btw).
I haven't heard this vamp anywhere else but it kicks ass so I'd like to hear it more. Does anyone else happen to know where it has popped up, or know anything more about it? I just finished listening to all the shows with Vinnie from 1978-1980, and I could easily have missed it, but I don't recall hearing it any other times.