Only differnce may be in the drain plug for the pumpkin. Seems to be located in different locations between models.
There were a few 67's with 31 spline axles. I got one from a former Cobra Jet powered car (hulk). The gears in the pumpkin seem to klobber things in a standard axle housing. If you stick with any one the numerous 28 spline axle versions it will fit w/o modification.