umm... dammit, I swore there was a tech article on this.
Consider a few things... van or dually 14 bolts have different spring perch widths, so be sure to get a 3/4 ton (or 1 ton SRW?) 14 bolt.
You'll need to do something creative for the driveshaft -- a combo Uijoint, I think.
Also consider that the 14 bolt will be 8 lug and your front will be 6. You could carry two spares, or none... or switch the front to 8 lug, same parts as a D44, IIRC. Adapters are available but aren't cheap -- prolly cheaper to convert the front over.
-- A