Caster is always positive!
Negative caster would result in dramatic instability, the wheel not returning to center without being directing by the steering wheel and positive camber gain (instead of negative gain) during steering throw.
I like to recall what an old mentor once told me "Caster is faster"
For go-fast applications where steering weight is not the main priority for driver comfort, one should pretty much always target max caster possible. In my situation, with stock ride-height I don't benefit from the negative camber gained by reducing the static ride of the car, so to be able to get my target -2.5 degrees of camber, this meant that with the adjustment maxed out on the control arms 7.4 degrees of caster is all that was achievable. With a lowered vehicle it would be possible to get more caster for the same camber settings, I've seen 9 degrees mentioned on this forum for one track racer.