First, put a few more specs about your car. What year? Production month, if you know it?
You can kinda wing it. Every sprocket with teeth will have the v-belt side; every smooth sprocket will get a belt back.
I picked at random a mid-'92 M50. Here's the ETK diagram:
http://rust.mine.nu/bmw/showparts.do...=18&x=57&y=189
It shows the belt routing. Also... if you want to have a good ready resource on your E34, pick up a Bentley's E34 manual. I think most BMW dealers have them, but you can find them cheaper online. They're weak in some places, but most of their pictures, illustrations and procedures are based on the M50, so you should find lots of stuff directly pertinent to your car.
-Andy