Here is some info and a link.
FRONT AXLES
First of all, let me say that I really recommend no smaller than F250 running gear for weight carrying, braking and width reasons. You may get by with an F150 front axle if you have a smallblock motor, stock 15" (235/75R15) tires and carry little weight (not a camper, no winch etc) but it is a marginal setup in my opinion. Ford E350 vans are readily available and are the best platform for one of these conversions.
The Dana 60 front axle from an F350 or HD F250 is not so readily available but would be my first
>If the Vans, Bronco & F-Series are different widths, what front axles do you think will fit?
I used a 78 F250 solid front axle with leaf springs but I like the idea of IFS and coils for highway comfort. I had considered the idea. I would lean toward using no less than an F250 IFS for width. If you cut the centre IFS crossmember out it could be welded or bolted into where the present van crossmember is. The rear radius arms would connect close to the original van points. After 1990 F250s used leaf springs. Rugged, but coils ride better. The E350/F250 upper coil pockets measure pretty close but I am not sure how the coils would fit to the axle.
http://www.glinx.com/~sbest/4vanfaq.htm
