At the risk of saying the obvious Chris Scow of Trains Unlimited would probably be the most obvious source, but I don't remember when he started his Guatemala tours. The last one George Werner and I ran was in November 1980, and by then the railroad (and the country) was seriously falling apart. Traffic on the railroad had fallen to the point the available diesels could handle it, and track condition was deteriorating to the point where safety was an obvious issue. On a driving trip to Antigua my wife and I sat in our car at an army roadblock staring down the barrel of an Uzi held by a scared kid in uniform, that's when we decided it was time to stay away. I next returned in 1992 on one of Chris' trips, and it had only gotten worse. it was quite unsettling to see bridge ties missing on many of the big bridges. I don't remember seeing any regular freights in 1992. I was amazed when Henry Posner was able revive the railroad in 1999.
JBWX