It is a VA-50. The tank and all of the controls, including the plunger starting switch were mounted remotely. The "A" motors were used in the Aquaflyer boats as "Matched Systems". The 1930 smaller sized Aquaflyers used the smaller SA and PA motors and the VA was used in the 20′ version. I used to have a copy of the installations for the system.
Google "Johnson Aquaflyer" if you want more info.
Don