Gravity&air vs. hydraulic&spring
Hey Scott-
I have 4corner factory air-ride in my Expy... great for level towing and off-road clearance... but air springs only "push/lift". Going down is ALL gravity... and "how far down" is limited by suspension.
I suspect you want to "drop"... and primarily for show. So, maybe you really want hydraulics... which can push and/or pull.
With air OR fluid, if you want GT to "turtle" (wheels/legs inside with belly on ground) then you'll need adequate pivot travel at all 4 corners... and that would be with something totally different than what's bolted there now... not to mention re-routing exhaust.
However, if you're content with just being VERRRY dropped while stopped, it may be more feasible using hydraulics to pull/hold GT body down INTO existing spring load (maybe just 1 cyl pulling down rear, & 2 more for each end of front leaf). Then, when released/moving, you'd retain drivability.
Gravity&air vs. hydraulic&spring - gee, just a MINOR consideration

: I understand GT a-arms aren't too forgiving of "extracurricular" activity... so pulling on them may result in bending and permanent alignment issues.
JMTCW of rambling
-Dan