i don't know but i just ordered 67-73 about two months ago and put them on.. so they do work. heres the link http://www.maverickman.com/Suspension.html?998088949680 i don't know cuz i got aftermarket ones. i would figure unless they were for the big block cars they would be the same.
Yeah, my interchange manual doesn't tell me what the difference is between different years of Mustang springs, it just says the part number is the same for 65-66 Mustang and all Mavericks. Maybe the 67-73 Mustang springs were painted a different color?
Maybe different spring rates as it is likely that the 67+ Mustangs were a bit heavier than the 64.5-66.