The S38 Motor swap is far from simple--do some searches here and on bimmerforums.com and check out m5board.com. Most everyone is going to tell you that you should just pony up and buy an ///M5. From what I have read about S38 transplants, you would basically need an entire ///M5 donor car to get all of the necessary parts off of it to transplant, and then you still have a 520 with an ///M5 powerplant.