Wow, that seems way long. My 74 Dart Sport was only 48 3/4 inches center to center on the U joints. Did you measure with the rear suspension hanging or did you have jack stands under the rear axle tubes with the weight of the car on it?
Suspension was hanging. New rear springs as well. It’s a 65. The original driveshaft that went back from the 904 to the 7 1/4 inch rear end was around 61 inches long.
