try and give marcus a call (sc&c) he has fiddled with making a 3 link for g-bodys for a while and is close to somthing sell-able as far as i know atleast, not sure if it will go to production, but since G and A body frames almost only differ in width i am sure he has some bracketry that could be used to mount to the diff, and some crossmember stuff...
give him a call, and dont tell him i said anything about the 3 link
( if you see this buddy, im sorry
)