From the few numbers I have seen the SS springs and the wagon springs were both 77N/mm(440LB/in). The Impala uninstalled height was over a inch higher and was projected to be 1/2 to 3/4inch higher on a wagon.
A set of stock wagon springs would put you lower than a SS but higher than a sedan. The stock sedan 53/300 would probably lower it a inch below stock but mess with the ride and handling.
If you have real SS springs you could finance a fair bit of your costs by selling them.
If you're happy with the SS springs ride, you can make them a touch lower by simply cutting them with a cutoff wheel. Reduce the springs free length half as much as you want the drop. If you go too crazy in the drop, them won't be stiff enough to keep it from banging the bumpstops.