A while ago, I rebuilt my GT's front suspension. There are several excellent threads on the topic, but I thought I would build a thread showing what I did to fabricate and use a front suspension leaf spring compressor.
So, to start, you don't HAVE to use a compressor tool to disassemble the front suspension on a GT. If you have the suspension still mounted on the car, you can "compress" the front leaf by placing jacks under each A-arm at the ends of the transverse leaf (the "spring eyes"; this might not work if you don't have the engine still in the car; the weight may not be enough). Then you remove the "spring eye bolts" and lower the ends of the leaf (make sure that the car body is still supported!). Then the rest of the front suspension clip can either be disassembled, piece by piece, while it is still on the car, or you could then remove it as an assembly and disassemble it on a bench. But you have to install it back in the car to reverse the process, and I have heard that it can be tricky to get the spring-eye bolts back into place using this method.
Since I wanted to do a complete rebuild, including sand blasting the components and re-painting them, I decided to build a proper GT Leaf Spring Compressor. The FSM (Factory Service Manual) provides a portion of a photo that shows the proper factory tool. That, and a photo posted by Stanley P. provided the template that I used to build mine.
First, I needed a device to clamp onto the leaf spring. Here's what the FSM show: