I have been reading this thread from the start. Remember, you asked for people's opinions and advice on a public forum. You got both. Not all of the advice you get will be to your liking, especially when people are loyal to a specific brand. That just comes with the territory. I am not trying to bash you at all, so please take it for what it's worth. The one thing that concerns me over and over in your posts is that you state, "I just want a factory like 4wd system."
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There is no such thing as a basic factory like 4wd system on a Ford van. If you decide to go with coil suspension, then you have to come up with custom coil buckets for the frame, and or custom coil brackets for the axle. All the suspension linkage needs to be dialed in to prevent handling problems. If you want any type of clearance between the engine crossmember and the axle housing, then you need to lift it a minimum of 4" and trim the crossmember. Again, this is because the van frame was never designed to be 4wd.
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If you want a leaf sprung conversion, then you can pony up for the Sportsmobile version, go with UJOR, or build custom brackets. Leaf sprung systems have the same issues with engine crossmember to axle housing clearance, and have custom frame side brackets. For axles UJOR uses unmodified Ford Dana 60's from 99-04 trucks, while Sportsmobile uses Dynatrac 60's.
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There is nothing basic about converting a Ford van to 4wd. That's why there are only a few companies that can do it. Any shop that says they can do it for $4000 has never done it, or is going to take shortcuts in design and quality. As for Javier, I have no experience with him. His rigs might be fine, but I know nothing about them. Others do, and they expressed their opinion based on their experience.
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The more I think about it, the more it seems like if you want a 4wd van over the Excursion, then a Chevy Express with AWD would be perfect for what you are describing. It's not a diesel and doesn't have the load capacity of a E350, but it has the room and factory AWD you were describing. I wish you luck. You are getting out there with your family, and that's what counts.
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Brad