How does this effect driveshafts for late model GM cars? If you are ordering a Spohn Performance Extreme Duty or Top Gun driveshaft you want to pick 1350 as your rear u-joint type. If you have a stock driveshaft you will need to get a conversion u-joint that goes from 3R (stock) to 1350. We have these available, see our Part #E-U3R1350.
For older model cars (ie. 64-72 A-Body, etc.) you will need to determine your stock driveshaft u-joint size and get a conversion u-joint from that size to 1350 to connect to the rear end, or order one of our Extreme Duty or Top Gun driveshafts set up for the 1350 rear u-joint.