I was being general..... so I'm not exactly sure.. BUT...
Now that I think of it.. you could probably take a E30 M3 header... and modify it to fit the exaust man of a 318.... just might take some work and know how. As for pullys.... you can probably find the demension of your own pullys... then compare them and the ones on a stock M3 or the same year... take what ever the under drive pully kit change... did for the M3.. and change the sizes of the pullys accourdingly.. and just find some pullys your self.
1997 E36 M3 1990 E30 325i