check out the ridewell corp site, featherride manual specifically shows the installation proceedure for their trailer axle kit that uses a common (inexpensive bag, used on bigrig tag/lift axles), also look at the other big rig suspension suppliers for ideas on how they set up airride systems and reverse engineer your own system. I used a 4 link system on the rear and radius rods&panhard bar front on my 4 wheeler, 14" adjustable travel @ each corner.
Firestone industrial and Goodyear list the engineering and application specs for their bags on the websites, rolling sleeve type bags (more expensive)have more travel length than the bellows type bags.
Check with your independant truck parts dealer, they can tell you what parts are (AA) popular/available.
The other option would be to swap in a system from the truck salvage yard, try to buy a"rear frame section" with all the hangers, links,ride height valve,etc attached and then transfer it to your frame.