Belize is too close to home for Uncle Sam to allow ANY agression, especially while the Cold War is still in full swing.
Sounds like a quick regime change is due in Guatemala City. Or a fast deplyment out of Ft. Bragg.
It may not have been right, and I'm just about sure it wasn't fair, but the America's were very much controlled, on the macro scale, out of DC (truth is, they still are) 1960's Cuba notwithstanding. Any leader on the continent who forgot that in the Cold War days got a rapid reminder. Screwing with Belize would be an invitation for a quick hello from the RDF.