The stock springs in my 1970 Coronet had sagged.

A pal had given me a near-mint take off set from a 1971 Challenger, so I took both sets apart.

I took the top leaf (under the main leaf) from the Challenger set & added those to the Coronet set, one on each side. They were the same thickness & length.

That got the car back to where it looked 'right' again.

Ever since then, I save old leaf spring sets, just in case.......