Until last year, on my '73 the A518 transmission had become the lowest part under the car and would scrape on anything over 4" on the road.
I tuned the car's height based on that, and a bit on the front tires hitting the fender lips on full steering lock.

Last year I installed full length Doug's headers and much to my dislike, they now have become the lowest point under the car with an extra inch.
I had to turn up the torsion bars a bit to make them clear the multitude of speedbumps I encounter every day.

The 1" bars prevent the LCA's from bottoming out, but I would upgrade to 1.06" mainly to be able to adjust the car lower.