[Cobra Dude]

I also vote for pinion angle, but they way I know it is that the end of the transmission should be perfectly in line with the pinion angle *during hard acceleration*. That last part is the tricky part, because the pinion wants to rotate upwards on acceleration, and exactly how much depends on hp, tires, suspension geometry and type of bushings etc. This is why it's a trial and error thing, and why you point it down a bit. Don't pay much attention to the angle between the driveshaft and the pinion, but really to the angle between the output shaft on the transmission and the pinion. Start with a few degrees down and adjust from there.

Cheers,
-Neil.