Nice shot John. as always. On my first trip to Guatemala in June 1970 I have a note in my caption book that reads:"Not as much steam as I would have liked, but more than I expected." The IRCA (FEGUA) was pretty-much Diesel. That year there was much more operating steam on the IRCA's El Salvador Division and the Ferricarrel de El Salvador (FES) was all steam.
On my next trip to Guatemala and El Salvador in January 1972, the IRCA (FEGUA) was almost all steam. The reason was, as you relate, because most of the Diesels were out of service. Of the dozen or so GE 3-Truck Diesels in the 600 class, only one (#608) was still in service.
In January 1972 the much discussed Georgetown Loop #40 (now at CRM) was in use out of San Salvador. She came north to Colorado in February 1972.