Some updates on recently found information:
I did find a Guatemala History site on the internet that gives a first hand account that the former Compania Agricola plantations were apparently reestablished in late 1972 as Bandegua including the railroad. There is also a photo of one of the 25 ton types in the same paint, so apparently the current FEGUA 300s came from UFCo/CAG/BANDEGUA prior to 1997.
This photo also popped up, which isn't hard to identify:
To add to the roster confusion - United Fruits attempt to renumber their diesels into a common system circa mid 1960s still has some holes in it.
100, 200 series - unidentified
300 series - Compania Agricola de Guatemala/BANDEGUA (there is some apparent overlap with small engines from Tela RR)
400, 500 series unknown
600 - Tela RR in Honduras
700 series - Chiriqui Land Co. - Southern/Pacific division
800 series - Chiriqui Land Co. - Northern/Atlantic division/Bocas Fruit Company
Note that they had already relinquished control of IRCA so there is no connection between the renumberings with them. And as diesels were later transferred (such as the 720) they may or may not have been renumbered.