I have a military version battery cut off switch behind the center grill bar on my 51 kaiser. I am able to kill all electrical power while it is stored in garage. I also have a battery tender 6v connected to battery directly with a wire extending a plug under the car near the bottom of radiator. I store the car on a lift. I simply drive the car on the lift, disconnect all battery power, raise the car, plug in battery tender from below. No more worries.
I just have no idea the rating for a 6 volt battery cut off switch or does it not matter? it's a pain to get to the military switch in my 51 without taking alot apart. I just need to hunt down a matching switch to install in the henry j.