Hi Pim and Leo,
The rear suspension of the TWR race cars bears little resemblance to the road cars. I had the privilege of poking around under the car that lives here in Melbourne when it was up on the hoist, and although the general layout is the same you would be lucky to find any standard parts. Brakes are 'free' on International Group A and the rear brakes are outboard (bearing in mind these are early 80s cars) and massive AP items, location of the suspension arms is very different, the arms are different, the hub carriers are fabricated items, etc etc.
What I liked the most about Allan Scott's book is that it covers Jaguar's racing program in broader terms than just restricting it to the XJS program. It was interesting to read about some of the politics involved in TWRs dealing with a company that had only recently escaped the 'clutches' of British Leyland and all that entailed. As an owner of an XJS and a 635CSi - the two 'natural enemies' in Grp A - it was also interesting to read about the 'cheats' that both sides used to stretch the regulations as far as they could stretch them without getting caught out! I think most Jaguar enthusiasts would get a lot from Allan Scott's book.
The rear ARB links attach to the 'U' shaped bracket welded on above the small end bush on the trailing arms - no need to get the MIG out (and if you did you would have to press out the small end bush).
Most of the Pre HE XJS V12s had a rear roll bar (in fact all up to a point if I remember correctly), removing it to turn the car into a terminal understeerer at the limit was a nod to the litigious US market where any car that oversteered was considered 'dangerous'. I'm not sure how plowing headlong into an oncoming car is a better option in court than getting your tail clipped, but, there you go
I guess they figured most drivers should know enough to back off the throttle once understeer starts, but with the very light power steering on the standard car I'm not sure that most people would be able to detect it before it was too late.
With a standard V12 front bar and the addition of a rear bar you will find your XJS is a little more 'tail happy', but it will also feel much more stable before you get to the limit and will turn in to corners much more nicely (important with so much engine hanging out the front). Try to eventually track down a V12 'sport' front bar to go with the rear one if you can as this will make the car handle like the pre-HE cars did - removing the odd 'kneeling' on an front corner the HE has.