[Pampered-Z]

This is so hard to explain without diagrams!

Because the car is lowered you also want to take into consideration the engine/trans now sit lower in reference to the rear then whem stock. You are reducing you drivetrain angle.

Pinion angle is relative to drive line angle, the difference between the crank and pinion, with the pinion pointing down.

If you don't have a true base on the pinion, you first have to know what angle the crank is on ( it is not parallel to the ground, it points down some degrees), and you can't reference the oil pan! You will need to use something like a square off the balancer hub, assuming it's flat, or measure the front center of the crank and the rear of the crank (could use the center of the tail shaft). So that you can determine the downward angle of the crank and transfer that back to the pinion to find the angle at which the pinion is at zero, then angle down the pinion -2.

Without know what angle the crank is on you only adding negative angle between the drive shaft and pinion you can be putting too much negative angle on the pinion which will stress the universals. This is why with a lowered car or aftermarket K-member you may need to shim the trans mounting bracket down or shim up the trans mount to being the entire drive line back into alignment to eliminate high speed vibrations or positive angle.