Probably the E-350 van is equal to the F-250 truck. Both will have full floating rear axles, and have the 245/75R16 tires.
The curb weight on the van will be a little higher than the F-250. I am just thinking that the higher GVWR of the E-350 will be required with your hitch weight and the weight of passengers and cargo within the van.
Also you might try to find a not extended length van. The extra distance between the rear axle and bumper will make even more weight transfer from the front axle to the rear axle when hooking up the trailer and applying 800 pounds or so 60" behind the rear axle (better to have the shorter van with only about 42" behind the rear axle).
Fred.