Nice, why stretch a 103" wheel base tho? Do you really feel its gonna be beneficial?
The reason to stretch is not dependent on the original wheel base of the vehicle. Any time you add lift and larger tires, you also change the vehicle's original height to length ratio. Once you start looking at larger tires around 37" or larger, your changing that ratio enough that you will start to hurt its ability to climb as it becomes more and more top heavy. By stretching the wheelbase, you can correct the ratio back closer to stock and vastly increase the climbing ability and over all stability off-road while still obtaining that increased ground clearance of the larger tires. Also, you greatly increase the departure angle.
I've even read that a stretch will really help a TJ on 35's, but its not really needed for anything under 37's, maybe 36's.
This idea is perfect for what Nate is looking to do. I would seriously think about just moving the fuel tank though Nate. It wouldn't be too hard to move it up into your cargo area under the X in your cage and then build a box out of something around 14-16 GA sheet. If you did this, all you would need to do is move the fuel line so you'd still be able to do it cheap.This would allow you to get more stretch out of it which would probably be better if your going to 40's.
Other option would be to move where you keep your spare tire by building something like this:
http://www.genright.com/ProductInfo.aspx?productid=RTC3300You could build it easy and use it to mount your spare tire up on the back of your cage just over your rear X.
Then, you'd have a whole new open area right in front of your tailgate. Using that space, you get a aftermarket fuel cell like this:
http://www.summitracing.com/parts/RCI-2161A/Then use an adapter for your fuel sender like this:
http://www.genright.com/ProductInfo.aspx?productid=APR1000That fuel cell holds 15 gallons of fuel and is the perfect depth for your stock fuel sender. The adapter from Genright (others make them too) allows you to cut a hole in the fuel cell and make the stock fuel sender a near bolt in application. There area a ton of write ups out there on how to use one behind a TJ/YJ rear seat using stock stuff. I can't imagine a XJ would be much different. I've seen them used a lot for sale too. I might even know where one is new for $125.00. If you went this route, you wouldn't loose any cargo space either because it would go where your spare is already sitting taking up all that room. I think it would look better, not that looks matter, with your tire mounted on the cage X anyways.
So anyways, now for the rear shackles. IF change your mind on the fuel tank deal, then this shouldn't be an issue. Your shackles would be set and ready to go. Just flip the springs around, build a traction bar, and your set. I didn't read anything on it, but I'd guess flipping them around would be between 5-7" of stretch? Them using your perches you could make it 1" farther back.
If not moving the tank, the quick, easy and effective way to fix the shackle issue is to move the mounting location to your rear bumper like the YJ guys do when they are stretching. I can't imagine you wouldn't be able to do this and it would really make it easy while allowing you to run your shackles however you want. Maybe build something like this for the back of it?
http://www.bluetorchfab.com/Product/846/BTF-Jeep-YJ-TJ-Wrangler-Rear-Axle-Relocation-Kit.aspxI know most of these links are for a TJ or YJ, but the same ideas can be used for your XJ. I do think you'd be better to re-use your current springs flipped around and put your money into moving that fuel tank and spare tire. I honestly think you'd be happier with the results when your done. I know you wouldn't get much increase in down travel this way, but that can easily be fixed with a set of XJ Revolver Shackles later on.
