http://www.bmwhaus.ie/forum/showthread.php?tid=3684

I would be all over the 3.46 medium Case if it's still available great ratio for any e36 really, but revs will sit a big higher in 5th on the motorway.

The 318iS uses a small case though so you will need a few more bits, someone more knowledgeable will be able to advise what other specific parts you'll need.