I just replaced the Starter on my '48 Mercury with one from C&G. I know you wanted just the Solenoid, however, I must tell you the starter from Early Ford Store (CA) was not just perfect, it was killer, very heavy duty, compared to the previous one purchased somewhere else. It was part # 18-11000-NGot my at napa
Just bought one @ O'reilly's for $14.95 including tax & the button on the bottom.