I have a Alpine CDM-7874 in mine.  Had to shim the front chassis 1/8" so it
would not jam up against the heater.  Specs say it is 7" wide X 6-1/8" deep.
I have also had Pioneer DEH series in my 82 Vanagon with no problems.

Pat Callaghan Jr.
87 Westy GL
Portland, OR.
www.cybcon.com/~patcal