Engine wiring harness, Distributor, coil, OP sender, and TBI are different for 84 vs 85-86.
Depending on several things engine internal are same or different because car options and/or recall/warranty engine replacement.
Other items covered in my Cave, Duke Quick Ref
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)