So I searched but was unable to find a definitive answer. I have a 1970 cougar xr7 302 and want to upgrade the rear end with a limited slip or traction locking differential. My question is, what size is the rear end in my car? and what is the difference between a 28 spline and a 31, and which do i have? and finally what is the gear ratio as well? Your patience is greatly appreciated. I am a recent convert from import cars!