Back in the 1970s, I spent a lot of time at the Eastern Airlines base in Miami, Florida. One day I noticed a B-727 in one of their maintenance hangars that had unusual metal disc-looking "patches" on the fuselage fairing just aft of the wing trailing edge. These "discs" looked like those on C-130s I had seen while in the USAF, and, curious, I asked one of the mechanics what they were. He stated that they were frangible coverings of the RATO/JATO bottle exhaust nozzles. He further stated that Eastern had 2 or 3 B-727s with RATO/JATO capability that were used on South American or Central American routes which featured high altitude airports. He couldn't tell me whether or not they had ever been used.
Cheers,
Grog