Put a set of Shrick cams in there so you can make higher rpm power. The only way to make big power from a relatively small displacement engine is with RPM (i.e., S54, S65) and the stock S52 cams drop off. Shricks have no downside -- smooth idle, no low end loss. They are worth 9 rwhp on a modded S52. Track oriented cams like Sunbelt and Evosport are worth 18-20 rwhp but trade bottom end power for top end.
With the Shricks and a full race exhaust (which you apparently have) and the M50 intake manifold, you should be making around 260 rwhp. With the Sunbelts or Evosports, about 270 rwhp. Your horsepower to weight ratio may not quite equal an E9X M3, but your torque to weight ratio might exceed it. The S52 has a very balanced torque to horsepower ratio at 240/236 stock at the crank.
I think you will have a lot of fun with the toy. The E36M3 is still a great car even at 13-17 years of age. I have one with over 500 rwhp and over 500 lbs rwtq.