In my 46 pickup I didn't have to change the length of the torque tube although the prop shaft/splines at the U joint could have been an inch longer, but worked ok. For the 40 and earlier you'll just have to try it and see, may be just right. Also this swap is made very easy in that the spines of the car and truck torque tube to U jt. are the same. As I wanted to stay 6 lug, so I stuck the 3:55 ratio 54 torque tube in a 48 passenger axle, which btw uses same brake parts as pickup.
Only other mods were to move the spring perch over to fit the springs, lowering block to get back to stock ride height and center the axle in the wheel opening.
