Let's define pinion angle in it's simplest form that most incounter on their cars.The engine and trans are located by the mounts,the rearend is located by it's mounting points.Depending on your type of suspension you can calculate how much pitch or upward rotation you need to best align the ujoint under load.The trans position is fix,so the rear u-joint is where the binding may occur and that is what needs the attention.As has been repeated many times,springs need 4 to 6 degrees negative of the driveshaft angle,ladder bars 2 degrees negative of the driveshaft angle and 4 links need only 1 degree negative of the driveshaft angle.We did a lot of testing and have videos of the the rear end pitch and upward rotation as the car was launched under load on the strip.You can view some of these videos on Bob George Racing on U-Tube.Most all racers,chassis shops and builders use the method we have describing to set pinion angle.We like many others understand there are other methods but we tend to stick with what has worked for us for over 50 years.To give an example our 65 Hemi has had the same driveshaft and u-joints for almost 20 years and thousands of passes.The KISS method of setting pinion angle is the lest complicated and works.