The problem with the limited depth of the radio area in the dash of the Vanagon is due to the housing of the heater blower.  If you use a heat gun to heat the plastic housing behind the radio, you can push it back and out of the way.  The whole in the dash is standard DIN, so basically any standard radio will fit.  
Regarding brands of equipment, I'm partial to Becker radios (when I'm not listening to my Uher reel to reel)  and Focal Speakers.

Sincerely,
Craig Rogers                                      '85 Wolfsburg Weekender
Ineffable Audio Unity Inc.
The song of Life envelops the timeless void. 
                 Its name is...IAU
Specializing in Uher tape recorders.
(914) 378-1606,  carogers@idt.net