What is your goal in these measurements? If for body panel alignment, I would mock-fit the fenders/hood and establish they are straight with the door and the body bolt holes are not bolt bound, as well as diagonal dimensions are correct. Shock mount position and K-member bolt locations would probably set everything within specs as long as there isn't a twist in things which gets into a totally different subject. The reason I question this is that it would be pretty hard to have a firewall measurement that is off unless it is severely damaged and the front measurement is set by the radiator support, so you could have a car that has correct measurements side to side but the diagonals are off, i.e., it was hit in the front and is a parallelogram.
