I had the factory springs on my 87 re-arched with a helper leaf added by a local spring shop. Car had a serious sag to it beforehand. Raised the car about 2" higher than what I wanted and it settled back down to factory ride height after a couple days - exactly what the spring shop said would happen. It held that height for six or seven years until I pulled the springs and went with new ones while I was rebuilding the entire suspension. They were still at the correct height when pulled and I gave them to another guy who to my knowledge still runs them on his car.

Either get the re-arched or call John R Spring and see if they have something that will fit.