Degins, i think a spindle with a repositioned pin that would lower the car would be a very good seller. by raising the the pin about 1-2" (i forget what the optimal distance was) in the casting but basically leaving the rest of the geometry alone would give a much better scrub characteristic as well as lowering the car at the same time while keeping the rest of the geometry essentially stock and workable. that also accomplishes better centering the wheel between the upper and
lower control arms which would allow wider wheels to be used and that is where the scrub radius comes in. it would be a compromise of course as anything
suspension related always is but there is not another manufacturer that makes anything like it the only option is to order custom Coleman spindles or the like.
if you could produce a spindle like that with the raised pin you would basically have the market cornered. i believe there is a huge market for it for the performance guys as the stock spindle is basically the only major factor in getting the early cars to really handle like modern cars. it would be like Bell Tech was in the 80's when they were the only company that made lowering spindles for chevy trucks, the entire market for lowered sport trucks grew up around Bell Tech spindles. i honestly believe that there is a large untapped market for lowering spindles for early mustangs. everything else about the mustang
suspension can be optimized with something IE: rack and pinion conversions, coil over kits, upper and
lower control arms with better geometry and stronger, strut rods, altered
suspension pickup points etc. everything is covered except the spindle. the aftermarket pretty much even has the rear
suspension stuff figured out with bolt in 3 and 4 link systems,
panhard bars, watts links etc. but again the limiting factor is the front spindles.
i think you should contact companies like TCP, Global west, Air Ride Tech, etc and see if they think there is a market for a good drop spindle. it's very likely that if you were to produce one that these companies would either offer as part of their front
suspension kits, offer it seperately or even it just put a link to it on their website possibly all of the above. i truly think it would be worth your time to investigate it.
as for the altered tie rod placement for the rack and pinion kits i can give you a rough idea of where it needs to be located. basically it needs to be relocated about 1.5" toward the pin and about 1" outboard from where it is now. you could most likely just add another hole for the altered placement to the existing spindle though a little extra meat around the boss wouldn't hurt. if you wanted you could just have one casting to cover to stock and the altered location and just not machine the altered location for the stock replacement version. even on the altered version you could still have the boss for the stock position or you could cut it off completely for a cleaner looking part.