I thought someone may find this useful:
I'm sure everyone else here who has a Chevy van can testify that finding info and/or aftermarket accessories our vans is difficult or don't exist. I've also heard the the vans share frames other models and others say the van frames are wider than the trucks. No one can cite their sources. I came across this PDF posted online for Chevy pickups. My approach lately has been looking at accessories for the trucks then figuring out if it will work for the van. For example, I'm looking to buy a bumper mounted light bar that was designed for a Silverado. I'm not certain if the attachment points for the bumper for the van are in the same locations. I don't have a Silverado sitting my driveway to make side-by-side comparisons and I'm not willing to spend hundreds of dollars to have something delivered to find out it won't fit. I've been looking for frame specs for a long time and finally found them!
It's for 2005+ vehicles and it is a large file at ~34 MB. I'll be under the van this weekend to see how these frame dimensions compare.