I see 3/4 and one ton vans towing things all the time. Heck, I see 1/2 ton class fords towing big trailers around, and they just have inline and v-6's depending on year. They dont last, but they'll do it a couple times.
Vans tend to have a lot more body roll, but as long as its fuel injected, and at least a 351 motor, I wouldnt have any problem towing with one.
Think about all those big class-c motorhomes towing enclosed trailers and jeep trailers etc etc. Just E-350 van chassis with a camper on the back. Most of the new motorhomes are using E-450 chassis these days, but still plenty of one tons gettin it done.
Vans are pretty bad about blind spots, and the cabs are cramped, and the engine is a pain to work on, but you get lots of covered space!
Dont expect more than about 14mpg empty tho, and less towing.