It seems like I need to do some catch up research on the jag setup but I deff think that the evo or subi rear diff is the way to go. Maybe even using the entire suspension.
As for the exhaust, depending on your tastes, you could run oval tubes for ground clearance dump them right before the rear tires. Or run one or two oval, depending on how much cross sectional area you need to equal the 3" round, and run them beside the drive shaft. I know of a few places to buy SS oval tube but each of them use a different process in order to form it, so that means a 3" round may be have the same cross sectional area as the 3" oval.
Does any one have some solid pics of the jag under body? Maybe quality pic links can be posted on the first post of this thread as a reference to refer back to as the conversation goes on. Sources would also be good if any info is posted. Basically instead of continuously talking about this, we could be building a data base for it too to distinguish solid facts/spec from misconceptions.