Rebuilding the front driveshaft with sealed joints from dennys driveshafts. Found this in the box afterwards. Needed? I don't recall ever seeing this before on previous rebuilds. Does it need to slide over the centering ball/propeller shaft?
it's the dustcover for the centering bearing, you drive it on the center housing , metal ring first. A 1 1/2" PVC coupling works as a driver in a pinch. You can run without the dust cover, but I would recommend using it.
This pic is of the pin side of the joint. If you shaft had a non greasable centering flange originally then you need that boot to help it seal. Now you can run a greasable centering flange in place of a non greasable but not vice versa.