I was hoping KLR250 would chime in but since he hasn't I will attempt to answer these questions.  I believe the internals for the differential are the same, in fact I remember reading some where where Jag owners were pulling the internals from older cars and adding them to the newer cars because the newer differentials were not as strong.

As to width and narrowing I would assume the width is basically the same as a series I II or III XJ6.  The reason being is that when I ordered outboard disc parts the half shaft I got from an X308 were the same length as the half shafts that I already had from an earlier Jag unit.  I don't think narrowing it it would be all that hard at all. Based on all the Pix I have seen  it is still a double(ish)  wishbone suspension where the UCA is also the half shaft.  The biggest challenge will be narrowing the stamped LCAs.  I think if I were doing it I would fab up a jig using the OEM LCA and then make some custom tubular lower control arms that way you can make them what ever length you need and still maintain the over all Jaguar design.

Mustsed wrote:

So, there I am in the same boat as KLR250!!

All attempt to locate a first gen. Jaguar  IRS for a friends '68 Mustang failed! The only Jaguar IRS that could be located is a second gen. assembly (according a telephone call with the owner and his description). Never paid attention to these units but looks like they will work too.

How are these differentials called and what kind of locking carrier works for them? What kind of spring/shock are you going to use? How wide are these and can they be shortened or did you shorten them? These are the questions in my mind and am not able to find these on the www.

I have no way to see that part before purchase and still looking for someone who could take some pics and send them to me but would be great if KLR250 would chime in and give some info on the 2.gen. Jaguar IRS.

Thanks in advance!

Mustsed

heya Musted, The diff centre is pretty much the same as the old, but run a ball bearing on the outpt shafts, according to guys in jag circles you MUST make sure you use a good quality brand name bearing on them as the cheaper bearings dont last long. Im not sure how tough they are, or if they are the same strength as the older versions, but according to people i have spoken to its all the same stuff inside. I have all the dimensions written down somewhere, ill have to dig it up. Springs im using are airbags from ride tech, on some cantilevers in the trunk. You can easily mount a coilover to the stock location, but in my situation im running airbags, and getting an airspring rated for the unit meant i didnt have the room for the 6" bag. I was fortunate ebnough to have my factory spring towers actually line up perfectly with the lower arm pivot. The only grip i hav with the later jag units is the amount of anti squat build in, the rear arms are angled down at the rear quite a lot, i still havent put a angle finder on, but with my pinion pointing 2deg up i have about 8deg angle (angled down towards the rear) on the arm. i think this is also designed for tow steer....