Suspension
Eventually I will throw some info here.
Coil springs - Round coils of steel, they are installed in the front of our RWD vans
Torsion bars - Perform the same function in the front of our vans as the coil springs, used in the front of AWD vans
Leaf springs - support the rear of our vehicles(steel and composite fiberglass: see Generations)
Shock absorber - Should really be called a damper, as they dampen spring oscillation
Bump Stops - Prevent metal on metal contact between suspension and body. Black - https://amzn.to/2UuUY00 Red - https://amzn.to/2QLQZgk
From 1" to 21", there are many ways to go about getting your van higher in the air.
Most start out with the most basic 2" body lift, which is super easy to do and doesn't have to cost much, see sub-pages below.
Buy a kit or piece together your own?
These parts are so easy to source on your own, that most of the time you will not want to pay 3-10x just for someone else to package the exact same parts and have them drop shipped to you.
If you really want to spend the extra money to purchase a kit, see the original http://www.overlandvans.com/
See here for Front Body Lift and here for Rear Leaf Spring Lift
Can I convert from composite leaf springs to steel leaf springs?
You sure can! There are many ways that you can do it, this is the way I have.
You will need the leaf spring mount from the front of the steel springs(you can also buy adjustable mounts from Overland Vans), the rear shackle(or adjustable shackles), the steel springs, top plates/u-bolts(or modify your clamshell setup), and drill your perches(or weld on new ones). You can see how I did mine in the Rear Leaf Spring Lift page.
What shocks are best?
Look at original ride quality or better and you will be happy. http://www.rockauto.com/en/catalog/chevrolet,2003,astro,4.3l+v6,1410398,suspension,shock+absorber,7556
Just tell me what the best are... Well it's too subjective to really compare, especially from different people with different modifications, terrain, and driving styles. Not only that but people tend to like what 'they' bought. Then you have the, I have been riding on crappy shocks for the last 30,000miles and any new shocks feel 10million times better then the non-shock they were used to.
In addition, there are very few people that have tried side by side comparisons of new shocks, usually it's a once and done deal for the next 60,000 - 200,000miles.
Recommended reading: Today's Technician: Automotive Suspension & Steering Classroom Manual and Shop Manual by Don Knowles
What about longer shocks for my lifted van?
See the Rear Leaf Spring Lift page.