About the Shelby drop and the negative wedge (by Pro-motorsports)... The traditional Shelby drop consists of lowering the upper A arm mounting point 1". This helps improve the poor geometry inherent in the original Mustang (Falcon) suspension design. Lowering the upper A arm by 1" should not cause binding, though it may (probably will) cause the ball joint to wear more agressively.
The Pro-motorsports negative wedge is designed to allow for lowering the upper A arm mounting point more than 1", where binding would become an issue. Pro-motorsports recommends lowering the upper A arm 1.75" to really correct the poor suspension geometry. The wedge fits between the ball joint and upper arm to change the angle of ball joint, thus avoiding any binding.
With regard to wheel diameter and the negative wedge, I've heard a number of different things, including the wedge being required with 16x8 wheels. I continue to believe this is backwards... I can only speak for my experience with my '70, but as I recall, the Pro-motorsports kit does recommend the use of 16" (or larger wheel), but I believe that is to clear the upper arm (at the ball joint). And, I would think, based on my experience, that it should be possible to mount a 16 wheel without the use of the wedge... the key is in using the right backspacing.
In my case, I can verify that I was able to use the kit with a 15x7 wheel, but the wheel can have no more backspacing than 4.5" (which is about right for my '70). I actually had to slightly grind the lip on the upper arm to get an extra 1/16" of clearance (just to make me feel better).
Hope this helps clarify, and here is a pic for reference...
The Pro-motorsports negative wedge is designed to allow for lowering the upper A arm mounting point more than 1", where binding would become an issue. Pro-motorsports recommends lowering the upper A arm 1.75" to really correct the poor suspension geometry. The wedge fits between the ball joint and upper arm to change the angle of ball joint, thus avoiding any binding.
With regard to wheel diameter and the negative wedge, I've heard a number of different things, including the wedge being required with 16x8 wheels. I continue to believe this is backwards... I can only speak for my experience with my '70, but as I recall, the Pro-motorsports kit does recommend the use of 16" (or larger wheel), but I believe that is to clear the upper arm (at the ball joint). And, I would think, based on my experience, that it should be possible to mount a 16 wheel without the use of the wedge... the key is in using the right backspacing.
In my case, I can verify that I was able to use the kit with a 15x7 wheel, but the wheel can have no more backspacing than 4.5" (which is about right for my '70). I actually had to slightly grind the lip on the upper arm to get an extra 1/16" of clearance (just to make me feel better).
Hope this helps clarify, and here is a pic for reference...