Another small update, I finally got round to ordering and fitting a new rear anti-roll bar. I had a 22mm one from the blue car but it wasn't correct for the black car due to different rear drop links.
Having the opportunity to compare the arb for 'C' shaped drop links to that for standard straight ball joint type setup, I was quite surprised at the difference. Although not massive I'm sure it would have had an impact on the car should I have tried running my old arb.
I imagine the narrow arb meant for the 'C' shape drop link set up would have upset the drop links on the 2004 car forcing them to be somewhat angled.
Even the designs at the end were pretty different...
Everything fitted up nicely and my eyes filled up with varying bits of debris, I even took part in the obligatory 'drop a spanner on your face' routine that every home mechanic should try.