One end or the other of a leaf spring has to be fixed.
Some people have made the rear of the front springs fixed and mounted the shackles up front like on a Jeep. There are pros and cons on both setups.
Along with the pinion angle, you have to worry about the caster angle on the front end. The more you tilt the pinion the less the caster angle will be on the front wheels which can result in death wobble.
If you go the shim route, get steel shins not cast of any type. Roger Brown will custom make you shims milled from steel stock. Weld them to the spring perches.
Here is his web page with a lot of good info.
http://www.4crawler.com/index.shtml