I was just wondering why on my 69 Mach 1's door tag, the Axle code says "9", and the Trans code says "X". The "X" code is not in the "Mustang Recognition Guide", and I'm wondering just what it is. Now I have come across a few early Stangs that these numbers are in reverse positions on the door tag, but I can't see this being in effect here. There is no "9" mentioned in the trany codes, nor is there any "X" for a "69" rear axle codes. So what is the "X" standing for?? Thank you.