Ray, like I posted earlier, if this one could talk!
I would be concerned about the structural integrity of a unibody car that's had the surgery this one has received. Starting life as a coupe means it doesn't have the stronger vert rocker panels and other reinforcing items that made the chassis more vert ready. The donor red sheet metal, left door and bent/damaged front end indicates the life this car has had.
The 83-93 Fox Mustang rag tops started life as coupes. Even with a Ford engineered and designed prep package installed at the assembly plant before they were converted to rag tops, they had assorted problems. Cowl shake and a general loose feeling to the chassis were common. I had a 87 and a 88 GT rag top and they had some terrible cowl shake.
Not sure what kind of a parts car this would make as far as trying to harvest the power train. Like DonC posted, if the engine has been open to the elements as long as it looks like it has, then you could only plant some flowers in the 4bl holes and use it as a planter. Identifying the top loader was another challenge as one came up for discussion a few months ago and none of us including David Kee could ID it. Evidently a unique Mexican supplied part as well as the Dana differential. I remember the clutch fork looking like something you would see on a F600 truck and a bell housing sourced from the first generation Bronco. This one would pose a parts nightmare if you tried to take it back to a as built condition. It would have be be a labor of love where money is no object. I know we all love our "Clydesdale's" but we also all acknowledge the fact that unless a R, J or C code car they just are not going to be a good return on investment.
Ray, do you still have any contact with your friend in Guadalajara? Do you think there would be any chance of finding out why the Mexican government only allowed the coupe body style to be built until 1973?