New Coil-Over Conversion Suspension

Since the argument is often made that OEM geometry is just as good, potentially better, than many of these COC’s, but not perfect/ideal, what is the limiting factor? Spindle? And what needs to be changed? If spindle, sounds like DionR and I share a similar idea of a fabricated upright with a Mustang rear wheel hub assembly. I’ve talked to Michigan Metalworks about building something and they’re all for it, they build them all the time for low riding trucks. Build into it a bigger brake option like a Mustang four piston caliper so everything is available off the shelf at your parts store of choice. So if it’s spindle, maybe it’s time to figure that out and get something done? My Suspension Analyzer is long gone for the similar reason someone else mentioned or i’d plot it myself and play with different ride heights and moving the ball joints around. And couldn’t this same idea be used for a front steer rack conversion with a custom steering arm? Other things would have to change in the LCA/ball joint but that’s probably solveable too?

Suspension Analyzer is only $300. So what if 10-20 of us chipped in $30-$50 a piece (cover software and a bit for time), someone downloads and plots it out, gives feedback to the group, and we all know. Then we all finally have all the information needed to make the best decision given intended use, and we know exactly what parts are needed to accomplish the task. And we also have the opportunity to unpack COC’s and know what they bring to the table for geometry. Seems reasonable to me, I’ll throw money in. Heck, if someone near me has a rack, we can use my car to plot it, then jump on a zoom with some of the great suspension minds here and go through it together.
I'm sure I'll get railed for this, but in my opinion, the spindle is the limiting factor on both torsion and CoC. This is the reason we go for the FMJ spindle and some even use taller ball joints with those. Not to mention the limitation on brake options and you are still stuck with traditional tapered wheel bearings. While the brake and bearing situation is good enough, why not have an upgrade there when everything else on the suspension is aftermarket or "improved". On the CoC, I doubt there's a one size fits all there. I chose to go with the CPP M2 spindle that accepts the corvette hub and corvette brake. This opens up tons of options for brakes and I get the benefit of the robust hub and an option to have a wheel speed sensor. The problem is, CPP didn't offer a tall version of the spindle. To me, this shows what their target audience is, hot rodders. The Wilwood M2 spindle is slightly taller than the spindle I have, but the only option is tapered bearings. I'm not familiar enough with that spindle to comment on brake options.
Unfortunately, I don't think there's a big enough business case for anyone to invest the time and money into making a custom spindle for either setup. We need to come to grip with reality that classic mopars are either at the car show or drag strip. Those guys aren't worried about camber gain and roll center. If someone is dedicated enough to the brand to drop big money on building a "racecar" they will likely replace the entire front clip or chassis with something like that Speedtech piece. At some point, there's no reason to re-invent the wheel.
The benefit of the CoC kits, is we aren't limited with the lower ball joint like the stock stuff. As I mentioned previously, I'm sure a GM spindle would work, especially on my HDK since I can adjust everything, I just don't want to spend the money to try it.