I have a 1989, but since my car was NA, it didn't have the 3pc spoiler, so mine would be the same as yours.
When my power antenna died, I went to Canadian Tire and bought a $60 generic power antenna. I used the pieces from the stock unit on either side of the metal, since the aftermarket antenna did not come with anything of a suitable angle.
Bend the strapping for the lower mount into place, attach the drains to the factory provisions, and connect constant power, ground and the trigger to the factory wiring harness. I also have an aftermarket deck, but I connected the antenna out to the wiring harness on the other end, and I have had this working with a factory deck as well. (Bonus, if you use the correct line, you can get the antenna to retract when you change from radio to CD/Cassette.)
It looks just like factory from the outside (Since I'm using the factory fitting hardware after all) works great and costs less than 1/3 of a factory replacement. Even when the aftermarket one died (Antenna caught a plastic bag on the freeway) it was easy enough to replace with another cheap aftermarket one, and I'm still $$$ ahead.
