The new ARB is (again) from Down Under (Selbys/Whiteline # WHIBLF91). With a diameter of 24 mm, compared to 19 mm for the original one, it's quite a lot thicker and stiffer (actual roll stiffness increased by 155 %). Luckily it came with new polyurethane bushes to go inside the mounting saddles. The original clamps had to be widened a bit as did the dished washers that hold the end bushes.
Putting the new ARB under the car turned out to be rather straight forward. I used two trolley jacks for this, one under each strut so the car's weight is supported completely on the struts, thus maximizing the distance between the mounting holes for the ARB. As a result the ARB slipped easily into the holes of the track control arms.
The problems started when I checked the castor measurements. With the original ARB the measurements I took were 288mm on both sides. But I couldn’t get it under 310 mm, as a result of which the wheels were sitting far too much to the front of the wheel arches.