There were four styles of lower units on those classic alternate firing twins. This one was used from 1951 through 1954.
A redesign to make the motor less noisy included adding a bolt to the rear of the water pump.
In 1957 the pinion gear was reenforced to take the extra horse power of this 35 horse outboard. []color]
The introduction the “super quiet” outboards in 1958 included a thermostatic cooling system that included a larger water pump. This resulted in a wider gear case casting.
So the RD-19 is good – 35 HP, the RDS is super quiet and will not fit.
