My '64 C-30 came with regular stock springs that were a little old and sagged a little too much to my liking. I replaced them with new GM HD springs. It rode a little rough, sure, but that how it like them to ride. It put the front end up pretty nice, even when fully loaded with 5000 lbs of weight.
Funny thing is though, when I took the stock springs out and match them up to the new springs, the old springs were actually longer. After tripe checking the application, I learned that the HD springs length wasn't what was important, but the stout-ness of the springs themselves is what will raise up and strenghten the front end of the truck.
Bill
