Measuring for a driveshaft is an easy two-step affair. The first step is recording the distance from the lip of the tailshaft housing to the front of the pinion yoke. The second measurement should be taken from the lip of the tailshaft housing to the end of the output shaft. Measurements should be taken with the car on the ground, or with jackstands placed underneath the front and rear suspension. We did just that, but later placed the Mustang on the lift for illustrative purpose.