i'd just go with new ones, never know what kind of abuse/wear will be on 30-40 year old leaf springs and even uneveness from side to side. i think new ones run in the $100 range?
My springs were sagging back when we first restored the Mav... leaf spring helpers from adavnce auto parts... pretty cheap, and it sets the rear up nice. no problems with them either, and you can't really notice them at all. no wheel hop either...
Try reading the thread for "rear leaf springs". new springs will definitely raise the rear. I don't know for how long.