In addition for future searches...
An 84 deck lid will work with any 85-88 Duke powered notchback, but will have an interference issue with a V6 powered notchback due to the center vent design.
85-88 notchback deck lids will work on any year notchback, 84 included. You should probably not use solid 84 vent covers with the non-84 decklid.
Notchback and fastback deck lids will not interchange... unless you do something like this:Reality's Notched Fastback
[This message has been edited by carbon (edited 07-08-2013).]