Once the driveshaft was back at the shop I checked to see if it would fit. It did, but it looked too close to the TKO 600 transmission, so I called IEDS and explained what I thought was wrong. Turns out the TKO 600 input shaft is inside the tailshaft housing more than other transmissions. IEDS likes to have the slip yoke as close to the input shaft as possible to reduce the chance of vibration and transmission issues. They also stated that the outer seal is a dust seal and that the transmission seal is about an inch inside the tailshaft. I then checked the driveshaft during full drop and ride height and the slip yoke was 5⁄8 inch away from the input shaft at its closest position.