I copied this from the Express Savana Vans Yahoo Group.
http://autos.groups.yahoo.com/group/Exp ... vana_vans/
Chevy Express Van Body Lift by miltruckman (Bill Prestin)
I just finished doing a 1/4 inch body lift on my 2003 Express van. Why only 1/4 inch you ask? Well since I installed the custom bumpers and rock sliders (like nerf bars but stronger) along the sides. I had bolted them in place with just under 1/4 inch clearance between them and the van's body.
Since then, the van's rubber body mounts have compressed a small amount. This caused the bottom edge of the sliding door to just touch the top of the nerf bar when opened. The small 1/4 inch body lift was easy to do and cost only the amount of 12 large washers 1/4 inch thick. About $25.00, and I was able to re-use the original bolts. If anyone else does a lift on one of these newer vans, All you need is 12 spacers/washers (3 inch O.D. X 5/8 I.D.) in the thickness you want and longer bolts to compensate if the lift is over 1/2 inch.
The original bolts are 5 1/4 inches long and Metric in diameter. They are pointed and the threads do not go all the way to the end. I think if I went with a 1/2 inch lift I would go with the same length of replacement bolt in grade 8, as the replacement bolts would have threads all the way to the end. This would compensate for the change in thread engagement caused by the lift. Since the bolts would not screw in quite as far. All you have to do is pull all the bolts out of one side and jack up the body in the middle of that side. Then put the washers/spacers on top of the body mounts on that side. Then put the bolts back in and make sure they are tight. Then do the other side. Only takes an hour or so.
Keep in mind, when doing a body lift. The bumpers are bolted to the frame. If you lift the body 1 inch, you now have a 1 inch larger gap between the body and the bumpers. If you lift very much it looks kind of funny with that larger gap.