2 different types of splines, you have to have them in front of you, one is sharper and the other is lets call it dull, the 727 is sharp, the 500/518 and the 42rh46rh/re all went to the convo style and what happens is the splines in the slip for the con spline interfere with the straight inv of the 727 spline making it a TIGHT fit, which if this was a end yoke....not a problem...
The change in the spline cut was around 90 or 92
dennys changes part numbers so no one can help you other then them
