I've been waiting for Joel to pipe up with the answer to the 4spd vs. 5spd 
 Vanagon Diesel questions. I know he has the data 'cause he sent me one 
 page of it for the wear index. Lucky for you folks, it was the one page
 that has the ratios for the the transmissions used in the diesels:

                            High gear ratio          ring and pinion ratio

      Dsl with 4 speed          0.85                      5.428

      Dsl with 5 speed          0.77                      5.428

  I calculated that a 4 speed diesel would be turning 3650 rpm at 60 mph and
  that one with a 5 speed  would turn 3306.

  The transmission code for the diesel  5 spd box is 094 DX. It was available
  from 10/82 to 11/83 according to a note. Data is from Bentley.

  Regards,

  Dave