It takes about 5mm of "machining & shimming" per 1 degree of caster.
Rounding off the OEM caster to 3 degrees, to get to 6 degrees (the pre-Ford spec) if that's your goal, would take 15mm of machining & spacers (5/8 inch). I don't think the ball joint can be "slimmed" that much.
Contact Marlin Jack about the steering rack (bump steer) spacers.