A buddy of mine runs airbags for his suspension on an offroad buggy. No leaf springs, it is a triangulated 4 link and I believe he got them off a cement truck. Fully maxed out hight wise, he has about 20 lbs of air in them. He has hooked up to trucks and biggies and used the bags to lift them with no issue.
For your application, you would need to add links I believe. I don't know if you have any form of traction devices installed, but since your doing ok as is, you might be ok.
The airbags ride extremely nice, but have 0 lateral stability. He had to make some massive sway bars to help control the sway. He has them set on switches so he can adjust them on the fly (he can take the scare out of steep climbs, and I like the adjustability.)
Mounting the airbags on the axle tube is a decent location. You don't want them too far inboard, but just inside the frame rails will be fine. Then simply bild a bracket off the frame to match.
I reliese you were probably looking for something more specific, and this information is likely more advanced than you want to go with an air bag system as you want to keep your spings, but figured I would share.