URGENT!!! PLEASE HELP!!!

[ultrastang]

I installed a 9-inch rear,in place of my stock 8-inch, in my '68 Mustang. The only thing I had to change was the rear drive shaft U-joint. Ford used two styles of companion flanges: the 1310-series, and the 1330-series flanges. The 1310's are 3 3/16" across, where the U-joint cups seat into the flange. The 1330's are 3 11/16" across. I used a 1310-series flange from a Ford F-100 pick-up. The truck companion flanges are shallower than ones you will find on full-sized Ford passenger cars. My car's driveshaft measures 51-inches, center-to-center, from the front U-joint eye to the rear U-joint eye. If you use a 1310 flange, Napa U-jiont p/n 369 should work. If you use the 1330 flange, Napa U-joint p/n 353 should work.