While searching for the Western Airlines 2605, Mexico City, 1979 accident I discovered that there is nothing at all on the web. It is like this crash never happened.
Summary here:
http://www.ntsb.gov/doclib/recletter.../A80_59_60.pdf
The investigation was, of course, under the jurisdiction of the Mexican authorities and I've never seen a published report. Having said that, I have a copy of the NTSB's database for that period, but that doesn't really throw much more light on the circumstances.