I hope it works out, I'm curious how the box handles for you, be sure to post here afterwards!
So I pulled out my last alignment sheet from about a year ago and my caster was 5.9* on the driver and 6.3* on passenger. This was with my front driveshaft removed when I was troubleshooting my return to center. When I got home I measured the flat spot on the front of my diff at 87* which equates to a caster of 6* based on the information that used to be on this site -
http://go.jeep-xj.info/HowtoAlignment.htm (appears to be dead now). It basically stated for a HPD30, the caster angle is 9* offset from the pinion/diff angle when at 0*
View attachment 72863
I used this reference point to then set my caster to about 5.25 (86.25* on the diff) which is how it should be sitting right now. I'd like to verify this with an accurate method.
I searched around for accurate ways to measure caster. I understand that caster is the axis between the upper and lower ball joint in which the knuckle rotates on. I've seen methods that involve dowels inside the ball joint holes in the axle C's but that is not feasible in a situation with everything installed. I stumbled across one of Blaine's posts on another forum
I have a digital angle finder and I've tried using the lower ball joint flat in the past without luck but will try agian this weekend. In theory the lower ball joint flat should match the upper ball joint shoulder right? This should be a good way to verify my measurement