Have you looked to see if the 1998 4x4 truck parts will work on the 1999 van.

 

You can get about anything to work if you want to bad enough... :-) ...but it'll take major fab work. the van unibody rails are quite a bit narrower than the truck frame, to thin to bolt a lot of stuff to, curves downward over the front wheels rather than upward like the trucks (leaving no room for axle, springs, etc..)... The pics of the Quigley conversion posted a few days ago is probably the easiest / best way to do it, but I would want a lot more frame reenforcement to the frame and mount areas than it looks like they did (I'm kinda hard on things and tend to "overbuild" by many folks perspective)...

Note that there's more detail above earlier that almost nothing was bolt on. The 2500 and 1500 series trucks are very similar - ie the axles from those years mostly bolt right up aside from the rear spring width (2500 has 3" rear springs)... (not giving you grief, I know its been a few weeks). Time to go weld some more plating on my "frame" rails and start cutting the better axles out of the 2500... :-)

 

Nice setup, where can I get that same roof rack for my old van? I've got a 2000 1500..