Rock2pus,
you got any pics of that nissan? Im building a scca nissan truck also. Im running 17x7 with a 225 40 and a 17x8 with a 245 40 tire.
I dig the idea of a auto x cherokee. I have discussed this with a few road race buddies while working on my esp camaro.
What if you ran an add-a-leaf instead of a shackle. That should stiffen up the rear a lil more.
For shocks check out qa-1 as they offer many of there shocks with any combo of pin, eye,and t bar. Get me a demension at ride hieght and I can get you a partnumber if youd like. Check out a few dirt track suppliers. we run a dirt modified and we use speedway motors out in lincoln,nebraska for parts. there catologs are free and have plenty of shock demensions in there. They also have leave springs with the spring rates listed. They my not work in complete form in an xj but may they could call there supplier and have some custom made. same goes for the front springs. They have a ton of front spring rates.
Hope some of my rambling helps.