Page 38 of my 88 GS owners manual describes how to aim the headlight.
I don't have a scanner handy but here's the gist:
- front axle 16.4 ft from a wall on level ground
- with the bike on its wheels and rider on the bike transfer the vertical distance from the ground to the center of the headlight to the wall
- make a second mark 5 cm or 2" below the first
- turn the headlight on low beam and adjust until the light/dark boundary to the left of the beam hits the lower line
That's a starting point from the fatherland.