As for pinion angle taking priority over caster, I would agree in a stock application. I mean how far off was the pinion angle on every stock hp dana 30 produced for xjs? If you set the pinion angle right, the caster must be close.
HOWEVER. In a lifted application, I think safety, driveability, and handling take prioroty.
Pinion angle may not be as critical in a trail rig as in a DD. I regularly drive the XJ at 70MPH and are concerned with both caster and pinion angle. The caster angle should always be as high as possible.
In my XJ's case, at 4"s of lift, it only gets 5° of caster, when the pinion angle i correctly set, using offset ball joints.
I need to swap the LP with a HP D30 someday. More projects.
In my application, the front pinion angle was critical to preventing front driveshaft vibs. After re-gearing from 4.11 to 4.56, 1° of front pinion angle caused tremendous vibs when the driving at or over 55MPH (with 31"s) or 60MPH with the 33"s. The same pinion angle, on the 4.11s, had worked fine to 75MPH, as fast as I drive the XJ.
The increase in driveshaft speed made the difference. Everything in the driveline was tight. New axle bearings, a new driveshaft and the alignment was set to specs.
Getting the pinion angle to less than .25° eliminated the vibs. As a test, I bumped it up to .75° and the vibs came right back.
That was about 5000 miles ago and it's still quiet and steers fine, the result of spending a lot of time adjusting everything in the front end to handle and steer correctly. Every XJ seems to be a little different.