As far as I know early gms vans had upper and lower arms with coil springs and shocks outside the coil on the lower arm in the front. Doesn't get any easier to bag the front.
Rear is most likely leaf springs so the easiest method is bag over leaf unless you want to start cutting up the floor for a 4 link.

 

HI.. thanks for the reply. Cant be cutting up floors. Is there some video/how to online for bagging this type of suspension system? Sorry a bit of a novice. thanks

 

look up Air Ride Technologies AIRoverleaf. they have kits and a video. you'll get the idea.

 

Awesome.. thanks! It is going to be an italian ice truck..but now to come up with a cool name for it.