[red82gt]

It's more likely that an 86 that doesn't have quad shocks was not an original 5.0L car, not the other way around. I've been under many mid 80's GT's and all the 85's and 86's had quad shocks. I've run into a few 84's that had slapper bars and some that had quad shocks. I even have a 7.5" rear in my shed that has quad shock brackets on it.
Also, only the 87 and 88 turbo 4 cyl. t-birds had disc brakes. The rest had 9" drums so this may be a t-bird rear end. A truck rear end would have the leaf spring perches.