Over time, the RB211 became a respected powerplant but in the early 70s it was a major headache, with frequent shutdowns and a couple of catastrophic failures with Eastern (one was while spooling up at the gate). Often the engines could not be started. Over time this was rectified. By the time Delta got them in late '73, Eastern had ironed out all the bugs for them
The L10 was offered with only the RB211. Lockheed considered offering the CF-6 as well but it would have required too much modification to the tail, so the idea was dropped. Daniel Haughton, then pres of Lockheed, stated that not offering an alternative engine on the L10 was his biggest mistake. (Second biggest mistake was bribing All Nippon).