Unfortunately you can't just throw in any leaf spring when doing a 4wd conversion. Many measurements have to be taken regarding eye-to-eye distances, front eye to center pin and spring widths are all very important when making a 4wd van. The reason for the front eye to center pin measurement is to keep the front eyes on the front axle from sticking way out past the bumper. The shorter the better. Since nobody makes good, cheap leaf springs that are readily available for vans to be converted into 4x4, the next best thing is to order a set for trucks. These springs (both front and rear) are originally for the rear of a 1978 F-250 4x4. Front 4wd truck springs are longer and thus place the front eye too far in front of the bumper. Setting up the front suspension should take you at least a few hours with some strings, a straight edge or two and a tape measure, angle finder and level. The front hangers need to be as perpendicular to the center line of the frame as possible in order to keep the steering/ handling geometry safe and sound. Don't skimp out and throw it together!
The springs are made by Skyjacker and are the SoftRide type. Before purchasing anything, we made many comparisons and took many measurements between several trucks and vans to find the springs that would fit the best. Click here to see an axle/spring comparison chart.
Ford 1/2 ton vans have 2.5" wide rear leaf springs. When swapping in a heavier duty axle, it will generally have 3" wide spring pads (except for GM axles). This means I needed to add 3" wide spring hangers and shackles since I didn't feel like making my own (and I want the OEM look). This set is from a 1985 E-350. Notice how they had to be placed lower on the frame to correct the pinion angle and to avoid the use of rear lift blocks. To keep things sturdy, a 3/16" piece of angle iron is bolted on the bottom frame rail and to the bottom of the hanger. Also, only 2 of the original 2.5" hanger's holes lined up with the 3" hanger's.
A few more pics of how everything is tied together.