Also i just think your finding things other than you problem. One of your first posts tells me something i am always fixing.You put shorter tires on and it got worse...not a brake,balance,tire or any of those. Back to frontend alignment. The alignment guys cant get enough caster in it. It needs 6 degrees and really dont care what the stang II specs are. I have fixed maybe 30- 40 stang II because of this problem.
The reason the it gets worse with smaller tires you ask? Puts more rake in the chassis and takes more caster out.
I will bet it pretty touchy steering also...another sure sign caster is wrong.
Check it yourself with angle finder on the spindle.
Largeman mustang II stuff is one of the worst offenders on this problem....cut a lot of them out after guys have spent large sums of cash on everything else