The problem is seldom getting enough negative caster. If you turn the rear cams all the way in and fronts all the way out to gain maximum caster the camber will usually end up in the negative range, The problem results if you desire 0 camber. Then the rear cam must be rotated out, to increase camber and reducing caster. It's a trade off of trying to get enough positive camber and caster. I have never seen much over 2.5 degrees on a B-Body after doing hundreds of them. I don't believe anyone obtained 5 degrees of caster without modifying the attachment points. The idea of shimming the lower ball joint will obtain negative camber but you still won't effect the caster reading much if any. To gain caster you must either move the upper ball joint rearward or the lower ball joint forward, if your out of adjustment then either the upper arm or strut rod need to be modified. Also as I stated earlier every degree of forward chassis rake reduces caster by a like amount. 2 degrees of chassis rake is not uncommon with lowered front end.
Doug