Rear leaf spring ride height?

When we first built the 1971 Challenger we used some recommended leaf springs from JC Whitney. They were perfect. I like to have the body line above the rear wheels horizontal not pointing down. Now my son put bigger 15" wheels and tires on the back. Where can I get leaf springs to lower back down a couple of inches so it's not so high in the air? Cost is a factor here.

Thanks, Steve
Author: SteveSS