Originally Posted by
bluetoy
It probably has a 9" rear. There's no cover to pull off. Jack it up, put the rear axle on stands and mark a tire with chalk. Mark the driveshaft with chalk. put her in neutral and crawl under. Rotate the driveshaft and count the turns until the tire rotates once. This assumes it has limited slip or at least both tires are rotating evenly. If not keep one tire stationary and rotate the driveshaft until the other tire does 2 turns. The number of rotations of the drive shaft to do this will be your gear ratio.
For the trans and gear selection if you have a 3 spd auto it won't be overdrive. If you go modern t-5 etc or a 4 spd auto they will have overdrive. It will allow you to run a better gear. your hwy rpm will still be low enough to drive it regularly but acceleration will be hugely increased!