The XJ40 rear axle is entirely different from the XJS and will not bolt in, and the diff is not compatible. Your easiest route would be to find an entire outboard rear end from an XJS, and swap the diff if the ratios on the replacement are not what you would like. Outboard braked XJS hubs can be fitted to the inboard setup, and maybe XJ40 hubs (not sure) but some of the fixings/fulcrums are not exactly the same and would need fettling.
Greg a 95-96 XJS IRS is difficult to find and expensive. There maybe a cheaper yet better way. I don’t know hence my questions.
I know the XJ40 IRS is different but it would seam not totally different if hubs and bracing (see FiBoys stuff above)can be used with the XJS IRS.
From one of the links I posted above “You can put X300 type outboard vented brakes on the XJS/XJ IRS. You'll need some XJ40/X300 half shafts, complete with hub carriers, X300 outboard vented brakes, and some spacers approximately the same thickness as the discs you are removing to make up the length.”
“If you're talking about the bearings where the hub carrier attaches to the whishbone, I've used the bearings that come with the hub carrier (i.e. XJ40) and the pin that was already on the car (i.e. XJS). All fits together just fine.”
The XJ40 hubs and drive shafts can be used to upgrade the XJS rear to OB brakes.
The main difference is the lower fulcrum shaft in the XJ40 rear is smaller in diameter than the XJS, so you will need to bush the XJS LCA's. The park/hand brake will need to be modified as well.
It WILL work I have mocked it up from the old XJ40 rear I bought for the gears.
BTW thew XJ40 had toe adjustment on the rear as well.
Be aware that the XJ40 hubs are weaker than the older style IRS hubs. A friend who is heavily into vintage racing warned me about that when I was talking about changing from inboard to outboard on my Daimler.
He said the hubs used for racing are XKR hubs and they don't fail in heavy use and apparently can be adapted.
The stronger hubs were the inboard brake XJS ones. He been racing/managing racing teams running Jaguars in the UK for 40 years, so I trust his opinion, but I have no direct experience. I gather he's seen multiple XJ40 hub failures in racing use.
Only hub failure I have seen was the inboard style on a DS420 limo in livery service. Mind you, a DS420 is ~2,000 lbs heavier than an XJS. I put my DS420 on a scale and the curb weight was 5900 lbs.
If you look at the XJ40 hub Jaguar added X ribbing in the rear of the carrier because the earlier hub carriers crack just above and parallel to the fulcrum shaft. The X bracing in the later hubs prevents this.
The XJS turbo had this issue very early in its racing career but never cracked an XJ40 hub carrier, and believe me Bruce drove it like he stole it. I saw him come out of pit lane more than once and light up warm slicks.
Even on road cars the earlier hub carriers crack, google it.
