[shoooo32]

Considering we're discussing a 40 year old car that has likely experienced suspension and alignment changes since new, pinpointing the exact speed the car will break loose would be very difficult. Taking into account weather, road conditions, driver inputs, etc... this would be tough to nail down.

My advice: find a large, empty parking lot and slide the car around. You could attend a formal autocross, but 15 minutes in a parking lot will tell you what you want to know.