I will also verify the difference. I had to replace mine and bought the "universal" lines from the fiero store. Well, they aren't
really universal. The lines from the fiero store would be great for the 84-87 cars, but have to be re-bent to fit around the 88 front crossmember (and then the lines become the lowest point on the car...). The rear, engine ends of the lines were a little different from the 88's, but nothing difficult or that needed rebent.
BUT, Although I can't verify it myself, it looks like 88 lines would work ok for the older cars...
The reason is because the original 88 lines had a bigger "loop" to go around the front crossmember, and the 84-87 cars had a smaller "loop" to go around the front crossmember. Although it was tough for me to put the older lines on the 88 (not enough loop) it might be easy to go the other way (excess loop) when putting 88 lines on the 84-87 cars.
Since you're parting the 88 out, I'd try it before I'd buy it.
If you do try it and it works, please inform us so that we can tell the fiero store to change their universal kits accordingly and save everybody some heartache
HTH