I have a 68 Shelby GT 350 4 speed car. I am thinking about changing the rear gear, or whole center section, to a more highway friendly gear (currently 3:89). I figure I will have to pull an axle to see if it is 28 spline or not but I thought I would ask you guys. Is it safe to assume I have a 28 spline rear end or did Ford use the 31 spline axles very often?