I can put you in contact with the guy who has done this, the guy I saw at Mooneyes. He drives his van all the time here in So Cal and can probably go through all of the issues he came upon and how he dealth with them. He did this in his driveway at his house, not some fancy shop. I spoke to him at length on the phone.
I wrote the first paragraph, what i meant was c truck 73-87 5 lug lift spindles will work (if you can find them). The late model spindle will work, but you must use the same rotors, bearings and brakes for that spindle. A few older c truck owners have done this you can look it up on line. You can use the upper ball joint for the late spindles as the bolt pattern is the same (classic GM), the lower BJ I believe is the 30. I have both arms at this point to compare and not have had the chance. It's all about the BJ taper. One person complained about the tie rods hitting the sway bar, he put the tie rods in from the top of the steering arm on the spindle, but beware study bump steer.
I wrote the first paragraph, what i meant was c truck 73-87 5 lug lift spindles will work (if you can find them). The late model spindle will work, but you must use the same rotors, bearings and brakes for that spindle. A few older c truck owners have done this you can look it up on line. You can use the upper ball joint for the late spindles as the bolt pattern is the same (classic GM), the lower BJ I believe is the 30. I have both arms at this point to compare and not have had the chance. It's all about the BJ taper. One person complained about the tie rods hitting the sway bar, he put the tie rods in from the top of the steering arm on the spindle, but beware study bump steer.
Cutting and welding in the g30 ball joint flange in to the g20 arm took about 1 hr to do. I would not recommend doing this unless you're a professional fabricator.
So now my setup is stock G20 control arms top and bottom with ball joints to match a 88-91 lift C1500 spindle.
If I have to buy C1500 new brake rotors to fit the spindle that's fine. If I need brakes to fit the C1500 spindles I'll just grab a set from Pick N pull and rebuild them.
My only unknown is the tie rod ends. I'll update tonight.
As for the rear lift. 4" lift blocks are easy enough. At that length extending the break lines will need to be done as they are tight when the suspension is fully extended.
Also pinyon angles need to be adjusted with shims.
The drive shaft is just long enough but mine needs a balance so I'm going to extend it 1-1.5 inches just to know it's right.
I have the back wheels on and 35" tires clear fine with th a 4" lift and it look pretty rad so I'm looking forward to doing the front.
Ok so G30 lower ball joints don't fit the 88-91 C1500 spindles. They go in but are not long enough to get the castle but seated. So I'm going to the parts store tomorrow to see how much longer the C1500 lower ball joint is. I had them side by side two days ago but didn't notice the difference. I'll have to swap them out.
Off to Pick N Pull to get the C1500 brakes, baking plates, and break hose.
I'm going to need a much longer beak hose up front to get the brake close to being mounted on the spindle.
The biggest thing I notice is the spindle off set is about 2.5 inches wider than stock. So I would offset in the back rims to match if I was going to do this again. As it is I'll get a spacer plate and longer studs and call it good.
Well I got it all together today. Of course just when I think it's all done I realize I also need lug nuts to fit the C1500 hubs. The final parts list
G20 van stock G20 lower control arm with G30 ball joint flange welded in. G20 upper control arm
88-91 C1500 parts standard cab spindles 4" lift Outer tie rods ends Brake calipers Spindle bearing Crown nut, lock washer and pin kit M20 x 1.25 Lower and upper ball joints
Custom Parts 40" Custom brake lines front 25" custom brake line rear 9/16 x 11.5 x 3.25 round radius u bolts 4" cast iron lift blocks ( will need shims to align caster ) Ion 15" x 10" wheels 35" x 12.5" x 15" tires Shocks for a ram charger late 70's, 4" over stock from the G20 rear shocks.
M14 x 1.5 lug nuts
This set up will work for all G series. G30 no need to modify the bottom control arm.