WOOOO HOOOOO !!!!!
I love the older - style GM vans, having owned 3 myself.
Nobody makes a brush guard/bull bar specifically for a van so I had to take one intended for an older, pre-88 GM pick - up truck (with the flat grill)
The cheapie guards that bolt directly to the front bumper of the older pick-up trucks will fit with no mods. But they just are not very strong and will bend under a modest impact.
If you want a stronger one, .. get a real, frame-mount pick-up truck version and adapt the mounts. If one has a bit of metalwork experience, it' pretty easy.
For a roof rack, try an RV store. There are universal-type racks designed to fit full-size vans that are easy to work with.
They may be able to get a visor, too . although I hate such visors. These vans have such a big roof overhang that a visor really isn't needed All a visor is .... is a big gas - guzzling parachute that ruins the fuel economy of an already less-than-economical vehicle.
As for the suspension...... on your van, front and rear suspensions are virtually identical to the 2wd pre-88 Chevy and GMC pick - up trucks. One used to be able to buy lift kits for those trucks, but I think they have been discontinued. If you look around, you may be able to find one. The post '88 truck kits will not work.
If you just want to fix up the rear end........ look in the Yellow Pages for a shop that specializes in truck springs. Usually these shops work with big highway rigs. However, they can easily rework your existing leaf springs to make it firmer, and/or raised. IMO going to such a shop is better than buying springs on-line because any good shop can tailor the load carrying and ride height to exactly what you want.
Otherwise, GM offered 3 different leaf spring packs for this van...... 1/2 ton (too soft, imo) , 3/4 ton (just right) and 1-ton (too stiff unless you carry 1500 lbs of concrete in the back all day). You might be able to find the right ones one from a yard.
The problem with parts from old custom vans is IMO their poor quality. It's been decades since custom vans were really popular, so any old parts will likely be ancient crap that really wasn't very good even when new.