Here is a good primer on driveshafts and u-joints. Tom builds nice stuff.

http://www.4xshaft.com/techinfo.html

If your rear end (in the car) is leaf spring supported, you can use shims to change the angle. Shims are a wedge shaped piece of steel that go between the spring and the bracket on the axle . They are retained by the U bolts. CAUTION!! Support the car, AND the axle when you unbolt the axle.... dont be like the cartoon character who unbolts the axle and lets the car fall on him.

Shims are available in different angles.