In order to determine the size brake line for a 1990 Ford T F 150, you will need to know the size of your drum wheel cylinders. You also will need to know what kind of disc calipers you have.
15x7.5 inches with a 235 75 15 tire.
15 and 16 inches Look on door jam
24 mm i believe
GT's came with 225/60/15
The original wheel size is 15"
5 on 135mm