I thought the track width in the front caused accidents. it makes them very unforgiving at speed if you get a little bit out of shape.
Slowing down the steering some and push the wheels out to the edge would help. Also keeping center of gravity low.
If you are looking at a former P/S car I would think someone could identify it by the chassis.

a very short wheelbase and a narrow track width on a vehicle are two things that automatically cause handling issues with lots of power added.
slowing the steering ratio down helps considerably, as well as a small diameter steering wheel.
7-8 degrees of positive caster helps make the car go straight[er] than anything less, add 1/2 to 1 degree of negative camber and 1/8 to 3/16" [maybe 1/4"] of toe in to help [a little] when car gets out of shape.
all measured at a chassis "height" rise of 1 to 1 1/2".

I have zero bump steer and mustang II rack and pinion

if you don't mind me asking, what are your alignment specs ?