-SG- We already have the 1939 Instruction Manual on the site and thanks to Ian, here's the 1938 version. The main illustration shows the 'new for 1938' engine layout with angled push rod tubes and well known silencer shape.
The final full pre-war parts list in Ian's collection is that covering the 1938 range (click this link). The introductory paragraph on page 2 incorrectly states that it is for models subsequent to 1936 (should be 1937) so someone in the relevant department at the Works dropped a mild clanger!
Note that while we are all familiar with the abundantly available WD16H engine, this motor had been completely updated for the 1938 season. Apparantly the army stuck with the older model as they had a few thousand of these older machines already and did not want the complexity of stocking an additional set of spare parts for the newer model. Thanks for the loan, Ian!