Check out this site:
http://www.eatondetroitspring.com/ordering/They have front coil springs to lower our vans from 1", 1.5", or 2" for 200.00 a pair.
For the rear they need to know this info:
Are the leaf springs 1.25" or 1.5" wide, if they're 1.25, which mine are, then they need to know if they are the 52" or 54" long springs. He said to measure from where the springs mount in front and in back to the center where they bolt to the rear end. These are the two possible combos:
24" Front to center and 28" rear to center or
24" Front to center and 30" rear to center
They also need to know how many leaves are stacked in the springs. Seems pretty straight forward, he said with the 2" lowered springs the front ride is 10% stiffer than stock.
MB