I don't think a submersible pump with a tethered mercury float will
work, but I could be wrong. The ones I have seen at Home Depot can't
be lengthened long enough to reach the top of my pit; they would short
cycle as the water rises halfway up the pit. Besides, I would bet
that the float would snag on something on the way up or the way down
if it could reach the top of the pit.

By the way, thinking a little more about my current system, I don't
exactly have a pedestal pump, but rather some sort of hybrid system
with a submersed pump with a float tethered to a separate switch
assembly that is clamped to the discharge pipe that rises out of the
pit. I was thinking that a pedestal pump would handle the deepness of
the pit, but maybe a submersible with an appropriate switch system is
the way to go.

And just another idea, I suppose that since the pump is what I really
want to switch out, I could keep the existing switch system and plug
the new pump into it. Do they make a pump that relies on a non-built
in switch?