Will this be a daily driver? And if so, did you make use of that trunk space quite a bit in the Grand Prix?
I have a Notch, and I love my notch, but there are so many times I curse because I can't fit a whole lot in my trunk. [can't fit my 2 small slicks in my trunk] I used to have a 89 GT Cobra and a 91 LX hatch, and the use of the hatch was awesome... put my bike in there, had an 8.8 rear end I bought for the 91 in the hatch of the 91 with the seats folded down.
The Notches are the lightest, they have a look to 'em that people DO seem to like alot, but if the car has to be somewhat practical, but still a light as possible drag racer I say look for an LX hatch with little to no options unless you dont give a hoot about trunk/cargo space..
ALL Stangs from 1985 to 1992 are roller cam, forged piston motors and in late 1992 I believe they switched over to hypereutectic pistons due to cold start emissions regulations. 89-93 are mass air equipped [88 Cali cars were mass air].
Another thing to think about is, the T 5. From 1985 - 1989 or 1990 not sure, they were rated at 265 ft lb or torque. I think the year is 1990.. but the T5s got a little stronger and had a 305 ft lb rating. I wish I could find the magazine I have this all in but they had the T5s broke down over the year and I swear what I wrote here is how it was.
If I had to do it again.... i'd look for a very clean, low to decent mileage, 87-92 LX hatch with NO options. My 91 was a Calypso Green one and didnt have a single option, not even rear defrost, but it did have the black tweed interior...
Good luck!!!!