It all depends. Heres what I did on my 85. Ordered a duel exhaust kit from Summit, $250 I think, included headers/mufflers/and pipes that exit just in front of the rear wheels. Pulled the entire exhaust from the heads back, removed the AIR pump and all related hoses/valves/tubes/ect. Installed the new parts and done. NOTE, depending on the cross member you have this might not fit on the driver side.
if you keep the stock system keep in mind, in addition to the tubes going to the exhaust, you also have one going to the Cat that must be blocked off .
I have a torch, a grinder, and a 30 pack of beer, Yeah, we can make it fit..