The biggest challenge you will have is cooling. The XJ radiator is not up to it and in my opinion shaped wrong. I have the 4.3L V6, but am changing it out for the LS1. There is a video on Matts Off road when he solved his cooling problems. He swapped in the Toyota IFS steering box which sits outside the frame, then went with a 26X19" aftermarket radiator. Those can be gotten cheaply, and can cool up to 600 hp. To do it right you will have to alter the track bar by making it longer, but the stock track bar is under engineered anyway. The bell housing on the Chevy trans is bigger and will require you to do at least a 4.5" lift