Doug, increased high speed stability and self-centering of the steering isn’t the only benefit to increased caster. Increasing the caster in a Pantera also improves “turn-in” and reduces understeer. It improves steering “feel” too. If you competed in Autocross, you’d love it. Yes, it increases steering effort but I believe most enthusiasts would find the improvements worth the penalty. Ford likely did not.
From your lips to Ford's ears.
Ford nixed a bunch of suspension items which make me think they were concerned with creating a race car for the street that their projected buyer would be way over their heads with.
Brakes are another thing.
I autocrossed 40 years ago. Autocross settings are not necessarily if ever good for a street car.
I may "fool" with eps again in the spring (or sooner) and the auspices of that may reopen this for me again. Until then, it's closed.
I've done this, i.e., adding + castor, to other cars. At (only) +5° the tire was so recentered in the wheel opening that it would hit the fender lip in front on turns.
At this moment, I don't want to screw with that under the theory that if it isn't broken, don't fix it.
In that case, in order to center the wheel in the opening, I would have to split the difference and move the top a-arm rearward and the lower one forward. Then you may have a bumpsteer issue unless you bend the pitman arm down.
At this point, I can find grief in other places but thank you for attempting to share the joy and enlightenment you have discovered with me.