I am not familiar with English automobile vocabulary, so I can't think of the English expression just now, but I can explain what the German word probably means. Brüstung is the piece of wall underneath a wall opening or window (here the windscreen). Gurt is a horizontal stiffening structure . Brüstungsgurt is the upper horizontal beam right under the windscreen. In house construction that is where the windowsill is. I have found a suitable photo of the inside of a VW Caddy with a dividing wall and glass section. Hope this helps.
http://www.sparky.ch/autos/VW/Caddy-1.4/28327/