That switch looks like it has heavy contacts and terminals to be wired directly from the battery to the starter, bypassing the solenoid, but there's nothing saying you can't use it to activate the solenoid rather than the starter directly. In any case, If you install it in the floor, I would get some kind of cover to prevent the terminals from shorting against any thing, like the bell housing. The clearance between the floor and the bell housing is fairly close there.
