Caster is the angle realative to the upper and lower ball joints. More caster means the upper ball joint is further back than the lower.
When I was a kid I had a lowered VW beetle. When you lower them you end up with 0 caster. Twitchy as a mo fo. Hard to keep on the road and I always looked like a drunk driver. Besides the stinger exhaust that dang thing got me pulled over all the time. I finally got some caster shims to go behind the front beam. Made a HUGE difference. So I'd reccomend a proper alignment. Sounds like your missing some shims. The ones for the Ford go between the frame and the pivot for the upper control arm. PITA to adjust properly so when you have it done make sure to get before and after shots of the adjustment. Watch if possible. Slip the alignment guy $20 to get it done right. sometimes a 12pack of um, soda helps...
As far as adjusting the steering gear box goes be careful. Too tight and you'll smoke your steering gearbox. You need some play in there.
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