Quiafe Engineering's automatic torique biasing limited slip differentials (ATB LSD) enjoy some popularity amongst BMW owners in my area. I've exchanged some emails and have recieved confirmation from Martin of Racing Green Cars that their LSD for the XK indeed fits our S-Types. Here are links.

http://www.quaife.co.uk/differentials

http://www.thejaguarshop.com/Jaguar/...%20onwards.htm

Price is £895 (approx $1200) and an additional £600 for installation for those in Southern England (plus VAT).

 

Yup Yup, but Im not willing to take it on a gamble, of $1700 to find out it doesnt work.

So I've been emailing with Quaife and thats one of the persons the diagram I was is for

 

There is no need to risk $1700 here.
I bought a secondhand Diff (you can get these very cheap on fleabay), and had have taken all the measurements when I needed more info. You could also find 1 or 2 others that are interested and join ion the buy, but if you have the space, it could also be useful to have a secondhand spare anyhow, and you can re-sell it later. You should be able to get these units for about $250.
Another option is to send the money for a second hand diff to Tom from TL Jaguar in the UK (the other Jaguar Quaife reseller in the UK) and he will together with Quaife measure it up, safest and best solution imho.

 

I have a donor diff I'll be picking up and tearing down to measure up