There are generally 2 schools of thought on the 4x4 setups.
-Quigley is the kleenex of vans, they converted a ton of them and even non Quigleys are called "Quigleys". Their conversion was OEM approved and still to this day even the older stuff is well supported and you can get parts direct from Quigley. There are a few downsides though.
Limited travel - not really much can be done here, they wanted the van low for minimal impact to ride height and step in height and well, the driveshaft and front axle has to go somewhere.
Parts availability - Quigley modified parts and assigned their own part numbers to stuff. A lot of it crosses to other year OEM stuff, but some parts like the rotors are modified from stock so you gotta get them from Quigley or modify it yourself.
OEM Solution - Quigley was never intended to be hammered offroad, it was intended to provide a 4x4 van that met OEM spec. As such, expect it to be as good as a stock 4x4 truck of the same era.
Old tech - The Quigley stuff was done when the vehicle was new, so the conversions don't take advantage of improvements like can be realized going to later model Superduty axles.
Timberline and UJoint - They are the two remaining big players in the 4x4 Econoline conversion game and unless you have an well known and respected local shop, these would be the only guys I would consider. This isnt the place to discuss leafs vs coils, they both have their pros and cons. But in general, if you go with a Timberline or UJoint conversion...
Newer parts - The axles will be from late-model superdutys, so you get the bigger brakes, bigger bearings, bigger axles, modern bolt pattern, etc.
Designed as an upgrade - Design has been prioritized to be an upgrade and fix some of the ills of the Quigley or other oem conversions. Wheel placement, shock and spring rates, ride height, articulation, tire clearance, etc all are improved over what a Quigley setup can realize.
Parts availability - Timberline and UJoint use off the shelf axles with minimal/no modifications. My experience is with Timberline and they provided a parts list with the conversion so you are not locked in to buying service parts from Timberline and can source them anywhere.
When I see the list of parts recommended, there is definitely a bit of fleecing going on here because you showed up with a sweet new van and someone figures "this guy has cash"
1. 10 sparks plugs and coils (doesnt affect ride, not sure why recommended)
2. front and rear brakes (shouldnt affect wander unless the vehicle pulls under braking. If the brakes are good, maybe replace the pads, at least inspect them)
3. Ujoints (Where? Which ones? There are at least 6 U-joints on a 4WD van (2 on rear driveshaft, 2 on front drivehsaft, 2 on front axle). Unless these are blown up or obviously worn, no need to replace)
4. track bar bushings (OK this is a big one and will definitely affect how the van drives. This is a 30 minute DIY in your driveway if you have a new track bar. The track bar controls how bad the van will wander or get death wobble as it locates the axle side-to-side.
5. sway bar bushings (Probably needs it, if these are OEM Ford they are like 25 dollars and a 10 minute driveway job to swap)
6. Axle shaft assembly (The What? Need more details on the part recommendation and the reasoning behind replacement)
7. Center link (Cheap part, easy driveway replacement like the track bar)
8. Tie Rod remote and replace (Cheap part, easy driveway replacement like the track
bar)
9. Fuel Filter (Good maintenance idea, but doesnt affect how the vehicle drives. Not really a huge deal or expense)
Note that you will need an alignment after items 7 and 8 and could consider one after item 4 but not needed unless the steering wheel is in a different position.