Regarding Born Free, is it possible that the film score was recorded in the US, and that the re-record was in london--and that Barry and/or Sid Margo couldn't come up with the mini-cowbells?
Actually, both versions were recorded in London (at CTS most likely), Barry (reportedly) insisting that the film version of the cues were not adequate for soundtrack release (which is why we have the "highlights" album). My guess for Barry not using the cowbells on the album is that there might have been only one set for rental then and they may have simply not been available on the day of recording. Can't imagine him not using them because he didn't like their sound (he used glockenspiel on the LP).
I want to hear more about the rolling marbles though; that I hadn't heard about...
I don't know if this was just an assumption I made listening to the score or if I read about it in liner notes (which I would assume you would know about, Jeff, so maybe not). But it's pretty obvious to me that we're hearing an electronically processed small ball rolling - a steel marble or ball bearing maybe - in this cue:
Escape from the Planet of the Apes: A Little History - :15-:18, :32-37, :51-:55, 1:12-1:19
I must be mistaken about Twilight's Last Gleaming, as I can't find anything spot checking through the score. I thought it was in The Bubble, but I'm not hearing it.