[gearmesh, inc.]

Pinion angle specs you hear from damn near everywhere are so vague if you ask me. They all seem to be referencing earth level and assuming that engine/trans centerlines are all at the same angle in reference to earth level.

What you need when the car is under power, is for your pinion centerline axis to be parallel to the transmission output shaft axis. That way, as the driveshaft rotates, the arc the front u-joint swings in is equal and opposite to the arc the rear u-joint swings in. That way any vibration that is generated at one u-joint is canceled out by the equal and opposite u-joint swing at the other end.

An easy way to determine the angle of your transmission output shaft is to put your inclinometer on the top edge of your valve cover. This will be pretty much parallel to your engine crankshaft and thus equal to your transmission shaft centerline axis.

Stock suspension bushings will need more down angle set in comparison to the angle of the transmission shaft to compensate for pinion angle change while under power. I would estimate 2 to 3 degrees for stock bushings. If you have poly bushings, or heim joints, your pinion angle at rest will be closer to your actual trans shaft angle. You may only need 1 or 2 degrees of lower angle than your trans shaft angle since there will be less rear housing rolling under power.