I have not driven a Pantera with +6° Caster. Correct.
What I do know from other vehicles is that will increase steering effort, particularly while parking the car.
It is generally done for high speed stability increases for racing purposes.
That's how the Indy cars can run right up against the wall at over 200mph with a steady steering wheel.
I find it difficult to believe that anyone would put +2.5° in the category of a mistake by Ford? I don't see that and frankly, you don't have the credentials to question that, so stop trying to sell it.
I can understand where a wide body Pantera with 10 inch wide front wheels and285-50-15 tires could benefit from it simply because of the need for improved geometry in front on those cars.
Increasing the castor alone should calm the steering wheel giggling created by the bad geometry created by that wide of a front wheel.
I don't have that situation. I have a narrow stock body with 8x15 Campis and 225-50-15 P7's.
I just don't see the need for additional directional stability in my car at any speed. Sorry.
I would expect power steering to be a very desirable addition with that much additional castor.
I've seen the result of the addition caster settings on the R model Shelby GT350's. The steering in those cars is brutal. You can barely turn the steering wheel at all unless the car is moving.
Maybe what the issue here is the use of the word "need"? I'm not sure.