Anytime you move leaf spring perches you have to be concerned with ensuring your pinion angle gets sets straight. As a result, I spent a lot of time researching what my pinion angle should be.
http://67-72chevytrucks.com/vboard/s...d.php?t=375196
Unfortunately, I found a lot of conflicting information - but I got the most important parts. Your trans-driveshaft angle should equal your pinion- angle, and my driveshafts for the rear and front ends should enter the trans, transfer case and pinions within 2-3 degrees of each other to keep the force on my universal joints and resulting vibrations to a minimum. Since my new superlift leaf springs already came with a wedge to keep the pinion angle stock I decided to try to keep my pinion angle as stock as possible. First, I had to buy a magnetic angle finder. I bought this one (Spohn) off ebay for about $10 - works great. Then I checked the pinion angles of both housings before I began any cutting and grinding. I wasn't sure if my original 12 bolt pinion agle was stock because it looked like the spring perches had been moved. Basically I put the angle finder on the face of the 12 bolt where the cover sits and fixed it in place holding it at a zero angle. Then I measured the angle with the angle finder on the leaf spring perches. I measured -14 degrees and -15 degrees. This makes sense since the pinion should rotate up once the weight of the truck rests on the springs making that - angle zero. Since I'm going with a 6 inch lift I'll put my new leaf spring perches on at 15 degrees.