What mods are done to your car? I assume it is an 86-87 TR and it is running well? If it is then going to a 28" tall tire won't hurt it a bit as long as you are running mid to low 12's or better from my own personal experience.
I have run various gears in GN #1, 3.42 (stock) and they worked well, 3.90 (needed taller tires (28") to go as fast as the 3.42's), 4.88's needed 28" tall tires and using 4th gear to run the 1/4 mile, no quicker than 3.42's with 28" tall tires. 3.42's with 28" tires were quicker than 3.42's with 26" tall tires.
Good luck,