But how can you possibly know how much it rises under load? Any way to measure that? I'll update my original post to add that I have Caltracs and Calvert Racing mono leafs.
Depending on how your rear end is set up and or how soft your springs are it will vary of course that's why the article I posted tells you how to determine whether to move the pinion up or down: " If you accelerate and get a vibration OR your vibration increases then your pinion is too high. If you decelerate and you get a vibration OR an increase in vibration then your pinion is too low."
It took me a couple of tries (with different angle shims) to get the vibration to stop. But that's why the article gives these rules because it's really hard to see and measure how much your pinion rises when you're accelerating. There are many videos on u-tube where people have mounted a camera under their car to show how much the pinion rises and the videos show lots of variation depending on spring rates, spring lengths, ladder bars, 4-link, etc. Some pinions rise a whole bunch while some hardly any at all. I would recommend you start with making sure your pinion angle is maybe 1 degree less (down) than your trans angle (with the car sitting on the ground) because you know it's going to rise at least 1 degree if you have leaf springs. You know the pinion will rise but until you drive around and accelerate and decelerate with the new pinion setting you'll never know. You know for sure that if you make the angles equal it's still going to rise under acceleration just because of the load so you need to start below that point somewhere. GOOD LUCK and make sure lube those u-bolts.
PS - I used the solid metal shims that bolt to the springs this way they can't move or break like the cheap cast aluminum ones, in fact, I think I have a few sets left over (the ones that were the wrong angle):