Gathering hardware, parts and info for a 1939 W154 project. One of my sources is the MM Walkden Fisher article and dwg. I have also mined the web for photos etc. and am left with 2 unresolved questions.
The trailing arms on the 1938 version are clearly drilled. The 1939 arms are shorter, almost completely hidden by the wheels thus the presence (or absence) of similar lightening holes is unclear.
The Walkden Fisher plan shows ventilating holes in the brake drums, a common practice at the time, but I have been unable to confirm this from other sources.