Not a 100% sure agile does shocks for non 4x4 econolines, but it wouldn’t hurt to call and ask.
The difference between the fox shocks you get from agile and other fox resellers is that they will be valved specifically for the weight of your vehicle. Take your van to some scales and get weights for each axle, then provide that data to agile and they can custom valved shock for the exact weights of your specific van.
Bilsteins are great shocks, but they don’t offer anything specific to the weight of your rig. Just a generic shock for a stock van. If you don’t have a heavy build, they will likely be just fine for your setup, but if you’ve added a bunch of weight to your van, a call to agile would be suggested to at least compare pricing if nothing else.
"understeer is when you hit the wall with the front of your car, oversteer is when you hit the wall with the rear of your car, horsepower is how hard your car hits the wall, and torque is how far your car moves the wall."