Sooo I've spent a lot of time reading about how to squeeze power out of the M54. The winning combo seems to be an M50 intake manifold with port matching, catless headers, and cams. But you're still not looking at that much power. Sub 300. That being said, how much power do you really need? I have no problem keeping pace on a mountain road in my even slower 325, it lacks a little on the track but you're already ~35hp up from where I'm at. The chassis is the shining point for this car, and the M54 is actually quite reliable, and does sound quite nice IMO.
What I would do is whatever suspension mods you already have plans for, a limited slip diff (I'm very happy with my diffsonline unit), a ZHP steering rack (the yellow tag 712 rack. one of my favorite things I've done to my car, if not my favorite), and then the basic motor bolt ons listed above. Also maybe a BBK for the front, I've read that 330 rears are generally adequate for track use but you'd likely want a little more stopping power. At least it's not the pathetic discs I have on my 325.
What I would do is whatever suspension mods you already have plans for, a limited slip diff (I'm very happy with my diffsonline unit), a ZHP steering rack (the yellow tag 712 rack. one of my favorite things I've done to my car, if not my favorite), and then the basic motor bolt ons listed above. Also maybe a BBK for the front, I've read that 330 rears are generally adequate for track use but you'd likely want a little more stopping power. At least it's not the pathetic discs I have on my 325.