I have a 73 C20 LWB with a 2 piece drive shaft, I went to drive shaft shop once asked them about making an aluminum one piece shaft for me, the length should be close to the same as the 2 piece. All you have to do use a tape measure to check. Remove the rear U joint straps from the rear yoke diff and set it on the ground. Now, ignore the carrier bearing completely and using the tape measure, put the end of the tape at the center line of the U joint on the slip yoke of the trans, go in a straight line to the rear diff yoke and stop at center line for the U joint of that yoke. That will be your measurement. Removing the drive shaft from the rear end just gets it out of the way because the angles are a little different with a 2 piece shaft and measuring the 2 piece shaft wouldn't be as accurate because the middle part where the carrier bearing is also slides in and out. If you remove the end and set it to the side, measuring from trans slip yoke to rear diff yoke, it's more of a straight shot and then the only part that will slide in and out as it should would be the trans yoke, it's supposed to slide while driving. Make sense?
1
