Differential Question

If I'm not mistaken all A-body small block cars used the small yoke (known as the 7260 yoke). In 69 the 489 case debuted and they started switching to the cone type sure grip and at first the splines (10 count) were coarse. btw: the books say 68 was the last yr. for a clutch type but some were left over and used in early 69 so it's entirely possible to have a 69 489 case with a clutch type SG. I believe it was around 71 that they started using the fine spline (29 count) yoke so if yours is an original 72 A-body 3rd member it's most likely a small yoke fine spline unit. It's easy to identify what spline pinion it is by the size of the yoke retention not. If a 1-1/8" socket fits it's a coarse spline. If it's larger (1-1/4" I believe) it's a fine spline. As Tony said all the factory axle splines are the same 30 spline.