FWIW I would consider Michael/MG/Expovan's coil spring front 4x4 conversion. Thread here and website here.
Very high level thought, work and execution. He's also the guy who's wrapping up the final details on a 6.7 Cummins/Allison swap into his Ford van.
So i did a little more digging into the van and it has disc brakes in the rear end and it appears that my grandfather ordered it from the factory with 4:10 gear ratio and has a limited slip. The axle code is C2 confirming what I was thinking about the rearend (unless the website i looked it up on was wrong). A V10 with skinny tires and a lot of rain while accelerating on the on ramp equals a drifting van. The tires are new but not great in the rain.
another_mike, thanks for the input on the gearing. My last Rubicon that i had prior to my current one I lifted and put 33" tires on an it was a dog on the highway with the 4:10 ratio. In town it was fine but acceleration at highway speeds (past 65mph) was almost non existent. Then again it was the inline 6 and they arent known for power just torque. I wouldnt want to run into the same situation if I convert the van. A rig with a v10 that cant get out of its own way and or others would not be alot of fun.
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A 5-Star tune at around $500 will be half the price of a gear change and will wake it up and improve it in all areas. I did this to my motorhome and it scoots like a sedan now. I have a 98 v10 I'm doing MG's kit on and it will get the same treatment, but you can't go wrong with either DIY kit available. The rear full float with discs just says 'keep it' more and more to me. That's a great van!
Oh, Raptor Line the roof with a $100 mail order kit. Easy. Done. You can get the tintable kind and make it match your current color for a few dollars more in tint base from your local auto paint store.
Couple of things I want to point out. When you see references to newer V10 and the 5-speed automatics, those are the newer 3-valve engines. Without actually looking it up I think they have an extra 80HP or so over the older version you have. I remember an old neighbor who had a V10 motorhome and traded it in on a newer (and a little bigger) one. Went from the old 2-valve to the new 3-valve and was really impressed at the improved performance.
The general rule of thumb is adding 4WD eats 2MPG. Loose another 1MPG per inch of lift. Not always true, but generally pretty close.