[84LX89GT]

I know that '87-'88 GT's could come with No A/C, manual crank windows and manual door locks because i've seen a few personally. Pretty interesting. Although it sucks that they got rid of that option. I saw a "base"model '88 GT not too long ago that was weird because the door panels are just slightly different, so it threw me off. i believe that '87 and '88 were the last years where you could order T-tops as well and i believe they were phased out early in '89 model year as well.
Just some useless info.

Another thing about the heater core:
My heater core, took a dump as well and unfortunately,
my chilton's book explains replacing a heater core in a non-A/C vehicle to be harder because in A/C vehicle it says to remove the evaporator plenum to gain access to be able to remove the heater core, whereas i don't know how you'd do it in a non-A/C car. Although Chilton's may be wrong.
Good luck, the way i look at it, one of us is going to be cussing when replacing their core....and the other will be cussing and throwing things