To go to an 88 the DP will need a little rework. The 88 stuff we have done the exhaust housing is in a little different plane with the GTK stuff.
Did you get the warranty with those pipes?
The pipes have a 1 year warranty against cracking. IF it helps sale them for you, we will extend the warranty on these pipes to the new owner.
Good luck and if you keep them and need some refittment with the 88 let me know. I can cut you a deal on it.