If you want the clutch to work right, you need to make your own z-bar. Your observation about where the lower arm should be located is correct. The thing also needs to be at least heat treated but would be better to just reinforce it on both arms by doubling the thickness.
If you don't, it is going to twist like a pretzel unless you use it with the original 2600 pound clutch. That was never serviced through Ford. It was only a production line part.
The replacement clutch Ford parts sold was 2800 pounds. A standard street aftermarket clutch is going to be in the 3,000-3,200 range and will turn that z-bar into a wet noodle.
It would also be an excellent idea to replace the plastic bearings with real roller bearings.