If you plan to track the car, I think the most important thing you can do is put a roll cage on it. I had a major suspension failure on mine, which I will try to detail in another thread later. Fortunately, I was at an autocross going around 50 mph when it happened, and there was no real problem. Had I been on a track at high speed, it would have been VERY serious, as I do not have a cage. I seriously doubt that I will ever track the car again unless I put a cage in.
That being said, I'll describe the things I've done to make my car more track-worthy. First, the drivetrain. I have a sb 427 stroker going through a TKO600 and a 3.91 lsd. It puts 402 hp to the rear wheels. The 3.91 is probably a little short--a 3.73 would probably be better. However, with the 3.91 I can accelerate at around .6g in the 50-100 mph range. I have the .63 overdrive in the TKO, and I would recommend the .82 instead. the revs drop too much at the 4-5 shift and the engine bogs down. It's a great combination for the street, though. I need a diff cooler of some sort, though, as the diff pumps
oil out the vent hole during a hard track session.
When I bought my BDR, there was no such thing as a trackday option, so I had to modify the suspension myself. I put much larger sway bars on and replaced ALL the suspension bushings with solid monoball style. I also replaced the rear subframe bushings and differential bushings with solid ones. I installed adjustable lower control arms in the rear and set the camber to around -2 deg. I put fixed camber shims in the front to get around -2 deg. of camber there also. I am still on stock springs, but the race springs from BDR would be a good idea, too. I replaced the rear shocks with the Bilsteins that are listed in another thread. I run Hoosier R6s on 17" wheels: 245/45 in front and 315/35 in back. With this setup, the car corners nearly as well as my BMW M3 in track configuration. I got most of the suspension parts from Turner Motorsports.
I agree with what others have said about brakes. The stock brakes are very good if you replace the pads and fluid. I use Porterfield R4S pads and Motul RBF600 fluid. Be sure to flush the brake lines with large amounts of DOT3 fluid first to get rid of the DOT5.
Two other major things are on my wish list (besides a cage) if I am going to continue to track the car. The first is power steering. It is definitely needed. This car is a lot of work to drive without it. I get really tired during a 25 min. track session. The power steering has a faster ratio, too. The other thing I am contemplating is a front air dam/splitter (and maybe some kind of wing, too). The aerodynamics of these cars is really terrible, and I think some add-on pieces would really help at high speeds.
Hope this helps...