I was Director of Contract Maintenance Service at Eastern Air Lines in Miami in mid-1980's. One of our customers was Mexicana with their B727-200's. A few of their earlier ones had been fitted with RATO as mentioned before. Obvioudsly a necessity with -7 JT8D engines. Eastern had some early old -200 on the Air Shuttle and they were known as "Lead Sleds" on hot days even from the near sea level airports the Air Shuttle served.
We did "C" Checks" on those Mexicana aircraft but fortunately the RATO was long gone. One peculiarity of those aircraft was the ADF aerials which were usually in the bottom aft fairing of the wing root had to be remounted on top of the fuselage. Looked like a massive repair patch up there.
Saw a comment before that the writer thought some Eastern aircraft had been fitted with RATO. If so, I never heard of it.
Later, the 17R version of the JT8D were used on the high altitude airports in South America making RATO unnecessary.
My CMS operattion also did "C" Checks" on the RATO equipped DC-9 freighters (was it ONA?). They were under contract to the Navy for QICK-TRAN and required a extra boost in the event of an engine failure on T/O. The RATO was installed and active on the aircraft. These were scary for my techies were not used to having solid fuel rockets on the aircraft. I was told static electricity was sufficient to ignite them. Fortunately no servicing of them was needed. Did some extra safety training as the thought of those going off in my hangar was not something I wanted to imagine.