I did that on my '84. You need to install an axle shaft seal inside the pumpkin just outboard of the carrier. This of course necessitates removal of the carrier which means pulling both shafts (L&R). Might as well check wheel bearings, spindle bearings and all seals while your at it. The outer piece of the disco shaft has a huge diameter, 2 or 3 times that of a one piece shaft and therefore has a different type of seal, however, when you check out the stoutness of the disco set-up you may wonder if any strength is gained at all by the replacement. It does allow you to trash the vacuum stuff on the front end though.
1984 GW 360 NP208 SOA 35x12.50x15