Found a 320i at the local pick 'n pull that, strangely enough, had a 2-barrel intake manifold (someone had already removed the carb) and a dual exhaust (one muffler on each side of the car). It was NOT a 323i - had an M10, but I will gladly scavenge the necessary exhaust parts for you to convert your 320i or iS to a two-mufflered car. Looks pretty cool (exhaust appears stock except that the pipe immediately upstream of the rear muffler has another pipe joined to it (goes over the driveshaft if I remember right) with a muffler. Looks pretty trick, and whoever did it did a nice job of keeping things symmetric.