Now that I've had some real, hard driving time in the Mustang with the new suspension, I think I can offer a good write up of it. I'm fairly familiar with how it handles, but I will update as I better learn the limits.
This is one of the biggest points I can give praise to, since the improvement over the leaf springs and open differential were so substantial. The combination of adding Traction Lock (Ford's Posi) and a torque arm make the grip under acceleration incredible! No longer do the tires simply light up when I mash the gas. There is no squat, no drama, it just accelerates! Even when I do break the tires loose in the rain, it still accelerates. Just let off the throttle enough to reduce slip, which isn't much throttle. Tire slip doesn't make it move side to side either. It accelerates straight and true. No squiggles running down the road.
Switching from drums to high-performance discs in the rear certainly helped the braking performance, along with semi-competition compound pads. Braking is immediate and strong, with very little discernable pedal mush. Despite braking faster in this car than I ever have before in any car ever, I have not locked up the tires. Even in the wet. No nose dive that I've noticed, either. However, there is an interesting issue that I will remedy in the future: C-clip axles have a fair amount of play that pushes the pads out of contact with the rotors, leading to a mushy pedal for one pump after a hard turn. This seems to also cause some issues with hard braking after a turn where it pulls to one side. This is easily solved by swapping in 9" housing ends, but a temporary patch is to use residual pressure valves just before the calipers, and putting springs behind the caliper pistons.
As I mentioned before, the accelerating around a corner grip is pretty intense. Because I live in Washington, and it's the rainy season, I haven't had much chance to test the dry handling limits. That being said, I do get to test its handling characteristics near and beyond the limits more easily. On a couple hot corner entries, the back has kicked out fairly suddenly. I was hard on the throttle, and whipped the steering wheel into the turn, so that's understandable. But it was never unrecoverable. A flick of oppo always brought the back end in line. Otherwise, rear grip is high, and oversteer is easily controlled by applying throttle. The control arms cant outward towards the rear, giving it some roll oversteer. This makes for a more sporty feel, and I tend to prepare for actual oversteer much sooner than it will occur, leading me to drive more gently than I have to. Possibly most importantly, with the fully-rigid suspension, I can tell when the tires do what. A flick of the wheel will start turning the car, loading the tires. With my 60-series tires, it takes a little while for the tires to load. When that happens, I feel the chassis start moving in the direction I want it to go. All of this takes about 1/2-3/4 of a second. I think I could use some lower-profile tires. I can even feel the front end floating across the freeway while the rear stays straight and planted now. Before, the entire car moved and wandered, so I thought nothing of it. Now I have to do something about the front suspension. I will have to experiment further, but the curvy roads around here are unforgiving should things go wrong.
Ride and Comfort
Despite being a road-race suspension with rod ends and track-based Konis, the ride is still quite nice. I am running 225lb-in springs. Being canted inwards, they have an effective rate similar to stock. The track-tuned shocks are adjusted to their softest setting, which is still pretty stiff for street duty. But it makes the bumps feel much more controlled and eliminates any floating feeling. The NVH is surprisingly low, considering the use of rod ends. Yes, I can feel the bumps in the road, but they aren't harsh or clunky. I attribute a large portion of it to 60-series tires which insulate the suspension from the road. I'm sure if I put on some 17" wheels with 45 series tires, I'd feel much more of the road.
Overall, this is huge improvement over what was in the Mustang before. I know, that's not too hard, but it's such a staggering improvement that I honestly can't help but fly up to every stop sign with hard braking, and fly away from every stop sign almost floored. It's gonna get me in trouble soon.
Future changes will include a Lokar handbrake instead of the crappy under-dash unit, 9" housing ends, 3.73 gears after a manual trans swap, and a set of lower profile wheels and tires.