I'm talking bout the bit on the end with the smaller spline. ONe input goes all the way through the center into the viscous cartidge. If he has CV shafts, then it's no hass to butcher the inner one apart, and swap it for the two peice later model (R32 etc) and fit the 3x2 (etc) inner input flanges. Without the extra spline, the diff will just be open.
In a car that rocks UJ's the viscous caridge drive part needs to be welded, or otherwise attached to the input.