The two moulded plastic spheres at either end of the anti-roll bar (ARB) have to fit into the machined metal cups on the upper wishbones. However, the experience of others has shown that these can be tricky to fit. When I loose fitted one of the balls onto the ARB and offered it up to the cup, it was clear that it wasn't an easy fit. Indeed, the paint around the outside lip of the cup immediately fractured off the surface.
Two approaches have been used in the past: (1) to expand the diameter of the cup or (2) to reduce the diameter of the ball. There was only about 0.5mm difference between the two which was likely to be just the thickness of the paint coating inside the cup. Using the Dremel I removed the paint coating vary gently and a bit at a time knowing that the fit would change dramatically from tight, to loose with only a minimal amount of material removed.
With several fit, Dremel, and refit cycles, the ball was suddenly able to push tightly into the socket. I could then assemble the rest of the bar. This involved first sliding the rubber bushings into the brackets using some silicon lubricants. It's important to do this first, because fitting the bushings are much less compressible when they are on the bar. Silicon lubricant helps considerably.
Then the brackets and bushes can be slid onto the bar. Adding lots of lubricant to the bend area of the bar allows them to slip round and into position relatively easily. Then the rubber boots can be added to either end, followed by tightening the balls on the ends with a splash of Loctite. Adding a good smear of silicon grease (silicon so that it doesn't compromise the plastic ball) allows them to be slid into position in the sockets on the wishbones, and the mounting brackets can be tightened onto the chassis.