I am not aware of any customers using my 13" kit with dropped spindles. Without knowing who's dropped spindles and the design specifics incorporated into the design, and the precision to which they adhered to that design, I can't definitively say if there will or will not be a clearance issue, but I highly suspect there will be.
My 13" rotors are deeper than stock 88 rotors (which puts them closer to the lower a-arm), but they are 0.069" less deep than the C4 12" rotors that are also commonly used. The whole reason I developed the 13" kit was due to the common interference issues between the 12" rotor and the nose of the lower a-arm (88 Fieros only). This picture is the 12" C4 rotor, stock lower 88 a-arm, and stock ball joint:
While my 13" kit is 0.069" less shallow, the main reason it is "interference free" when used with the stock lower a-arm and the stock ball joint is the nose of the lower a-arm is always inside the recessed hat area and never alongside the pad surface area.
Lowering ball joints and dropped spindles by design lower the placement of the a-arm to the rotor. This will place the nose of the a-arm alongside the rotor surface eliminating the "interference free" benefit of my 13" kit and you are only left with the 1/16" of additional clearance vs. the 12" kit that has a known interference issue.
If the dropped spindles maintained very close dimensional tolerance with regards to the lower ball joint connection (but moved 1 1/2" lower), then you "should" be able to trim the nose of the lower a-arm (like recommended on the 12" C4 kit) to obtain the proper clearance. However, if the dropped spindle design alters the lower ball joint connection vs. the flange face of the wheel bearing... then it could be better or worse depending on which direction is was moved.
Here is the modification recommended for all 12" C4 rotor kits I sell. Doing this "might" give you the needed clearance to run dropped spindles with the 13" kit:
New clearance to the 12" C4 rotor:
Lowering ball joints change the movement of the lower a-arm nose for the worse (in regards to fitting larger brakes). From the pictures above, you can see the modification to the nose provides some clearance (about 1/8"). However, the lowering ball joints cause the nose to move closer to the rotor at a much faster rate than the stock ball joint, which can quickly use up the extra 1/8" of clearance and cause more interference. This is why I do not recommend lowering ball joints for either the 12" or 13" kits as it would require removing much, much more of the material on the nose of the a-arm, even then I am not sure you could avoid interference.
This picture show how the lowering ball joints change the movement of the nose of the a-arm relative to the rotor:
Hope this helps in your decision.
[This message has been edited by fieroguru (edited 06-03-2016).]
