G-MONC was actually on the German register in December 1990 (as D-ABNY with Condor), as was G-MOND (as D-ABNZ). So the only candidates for your flight (assuming it was one of the G-MONxregistrations) would be B/E/J/K.
MONB was never ETOPS was it? the other three you mention all were I think though. Would suspect it would have been ETOPS on that run.Wasn't there noe not in the MON* sequence - DAJB?