Am I driving you nuts yet. Big D mustang shop is telling me 67 stangs are heavier than 65-66 and should use 720, he says 620's are to low, he says his springs are custom made for them at BIg D. Now I don't want to second guess this guy he's been in business awhile, butAnother mustang shop is saying 620 is a 1" drop and the #s do not represent spring rates but heights. Anyone buy coil springs from big D? If so which did you go with? I am thinking go 620 if its to low change them out.