Hmm well with no sub-frame then you are pretty limited as to what can be done with stock components, as has been mentioned.
After looking at a couple of those vids posted above to get a general layout of the suspension I would bet you could get away with a couple inches of lift with nothing more than a spring spacer.
Yes you might limit droop a little but I would bet it would be just fine.
This type of suspension has a pretty good amount of travel for what they are.
I also doubt you will run into any problems with your ball joints.
Within reason your ball joints don't care whether they are at 7 degrees or 10 degrees as long as you are not at the limit of their angularity.
a lot of times with this type of suspension the shock reaches its limit before the ball joints will.
I suspect, as long as you are not ramping the van all the time, which might be fun but I also suspect you are not doing, your ball joints will be fine.
Other than that you are looking at either custom control arms or dropping suspension mounts.
From the looks of the upper control arm mount you could probably only get it down about an inch before running into frame clearance issues.
It probably would not be too hard to lower the lower arm mount a inch also.
You could do that and run a small spring spacer for about 2 inches or run a larger spring spacer and get 3 inches without too many other negative effects.
If you lower suspension mount though you may have to look into a dropped pitman arm to keep bump steer in check.
I would say look for a spring spacer or have a nice one made from some UHMW polyethylene and try it out.
You could always remove it if it sucks or do the lowered suspension mounts if it works and you want a little more.
Do some fender trimming and clearance for even more.
I assume you would be running bigger tires.
Obviously you will get a little lift in doing that as well.
