As you say, the trannys have a code stamped in a bottom edge that shows
what gearing it had when VW made it.

Page 3 of the Bentley shows where to find the code on the tranny.

Page 2 of the Bentley lists the engine versions that came in NA Vanagons
and below each engine type it lists the tranny codes that came with that
engine.

1.9 Digijet came with 2 different code 4 speeds, DU and ABD.

2.1 Digifant came with 2 different 4 speeds,  ABD  and ACW

Pages 35.32 and 35.33 show the internal gearing of each code for these 3
waterboxer trannys.

Mark
(NA Vanagons used a total of 9 different code manual trannys, I have
them all, 3 or 4 of some of them)

Page Dennis Haynes wrote:

>The 84 most likely has a much more optimistic speedometer than the 86 to
>the point that it appears to have a different ratio. There should be a
>stamp on the outside of the transmission. The DU came with 4.85. The ABD
>has a 4.83. The DK has a 4.57. I believe this was shortly used for the
>air cooled. The DM is 5.42 and the DZ was 5.86. These were Diesel boxes.
>
>
>Dennis
>
>