This may add fuel to the fire . . . 😆
The first rotary valve Speeditwins came out in the early 1930s – Elto Super "C"
It became totally Evinrude with the 6039 model in 1939. Three distinctly different lower units were used – yours is in the middle
That lower unit was designed for the Army Stormboat Motor – extremely rugged’ but a lot of drag.
Many trimmed off the "wings" for a little more speed.
