As a(n ex-) cyclist I have a number of c-spanners for cycle applications and some of those fit this application.
In fact have only just used one to re-assemble the refurbished water pump on a friend’s 1932 C4G which, I am pretty sure, has exactly the same gland assembly as the Traction. I did then loan him the spanner until the car is running but I shall see if I can “borrow it back” and take a picture with an indication of dimensions.
B………
Bernie