I haven't done this particular mod before, but my instincts tell me that if you are going to stretch the frame you should have a pro do it. Not only are you going to have to add sections of steel to you frame rails, you are also going to have to add sections or replace all of your rear brake lines, fuel lines, wiring, etc... Sounds like a big big job to tackle in a weekend. Can you leave the jeep at the welding shop for a while? You would need to. Then get on the internet and locate a diagram for the distances of the body mounts. You will probably have to add 2-4 body mounts to match the longer body as well. How good are you at welding?

Craig