93moparram has asked only to increase the height and not to increase the spring rate. You must understand if you add an extra leaf or add the Ranchero spring you will increase the spring rate.

If you only want, as you asked, to increase the height. Rearch the springs only.

To educate everyone on leaf springs. Think ofadjustable coil over springs. When you ajust the threaded collar you tune the ride height and the spring stays the same. Adding a leaf is like installing a thicker coil which will not necessarily increase your ride height. Unless it's as mention add and rearch but it will surely ruin the ride quality.

If you are using this truck to haul heavy loads a stronger spring may be what you need.