The dashes in the earlier models are different than the 80's models. The ac vents, and the dash openings are somewhat different. I believe that the overall shape may differ as well .Others have found ways to modify, but I haven't seen any of the end results. Have you considered filling in the crack and rebuilding the current dash?
My 87 dash was cracked in several places. I wasnt impressed with the aftermarket options (they fit and look like ass). I ended up experimenting with mine figuring if it didn't turn out, then off to the boneyard with finger crossed to find something else. I dug out the cracks, vacuumed the loose crap and filled in the voids with bondo. I overlayed the dash repairs with fiberglass and resin. I finally sanded down the repair areas and wrapped tweed over the entire dash. Since the sun in Az rots everything, I knew no matter what I did, it was going to be covered with some sort of dash cover.
Others have had good luck sanding down and filling the cracks with expanding foam, sanding down and applying coats of paint. Theres a write up somewhere on this site of different types of repairs and pics of the results.
