Optimize the rack mount bushings and Subframe bushings. Not all steering arms are straight . Maybe yours are bent? Not all tie rods are the same , maybe you have short studs? Maybe there are longer stud tie rods. 5/8 fine thread I think.
Read the rules as far as rack placement, tie rod ends, lower control arm bushings. Just moving the lower point a little will help. "Tolerance stack" is what you want to do. Move all of these points the legal maximum amount.
Lower is faster, deal with the bump/ The mustangs can be pretty bad. I fix a bunch of the street rods that are way off, and raced a bunch of circle burners..
IMHO. MM