I'm doing a 3 link on mine also. Using toyota axles, but other than that, its pretty straight forward. There are a few issues with XJ's when getting proper seperation measurements. Mine will have the upper on the pass side and will go up into the floor area just a little bit. Lots of frame strengthening for this also. I'm using rubber bushings on the axle end and Johnny joints on the frame end. (for all 3 arms).
be carefull welding the cast chunk to the steel tubes. I'd hate to see you make the cast brittle and crack later. It can be done, and should be done if you are running dana type axles but its tricky. Preheating and controlled cooling is a must in my opinion.