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.