Just finished a 5.2L magnum swap. pretty straight forward and definitely worth it, no modifications needed to fire wall or core support. But don't be fooled its just as much work as a 5.7L vortec swap would be. I would say go for it and do some research on a 5.2L swap because there are tons of build threads with tons of information. I pretty much did the entire swap from a hand full of build threads and a few PM's here and there. you can check out my build thread to see how the motor will fit. Since the 5.9, and the 5.2 are pretty damn identical.
these are a hand full of threads that helped me out a ton. good luck.