Any change in caster setting will result in a "toe-in" change in a Pantera front suspension.
Having owned a Griffith 200, I can understand your frustration with your 1971 TVR front suspension issues!
That was my point, that the castor re-setting creates a change in toe change.
The issue is that no one can state what that change is nor what the original toe change is.
Therefore by arbitrarily changing to +6°, you are going in blind and stuck with whatever the geometry change results.
Considering that castor increase is beyond what the original Dallara design provided for, why would I arbitrarily presume that is a good change?
That additional castor is also beyond what the original considerations were on the car. So there are stability improvements with it, but what are the trade offs?
I wound up also with just about the same positive caster of 2.7. I could get a little more on one side but I couldn't match them so it was limited to the lesser value.
I have similar camber values as well. -.50° was about what worked. The front doesn't seem to need any more but this is on P7's so I don't know what racing tires would need. Probably another -.5° or so but that's not an issue for me.
Rears are at just about -.75°. I don't want to increase the rear bite more at fear of the rear steering. Larger GTS rear bar. Stock front.
I'm very sure that the car was aimed at drivers expecting to be able to hang the rear out like a live axle car and being able to just back off the throttle if it started to get loose, predictably.
Some of you may like the 911's handling now but my 82 930 still had issues of trailing throttle over steer. The Pantera is much more manageable even with considerable power added over stock.
I'm still looking for what is considered a desirable limit to bump steer. I suppose the real answer is "as little as possible" and one should just hope that it can be acceptable?
This text uses -2.5°/m as the "target". It doesn't state that is desirable.