The best process that seems to work is to use the Citrus strip which does a really did job of removing the battleship gray paint on the floor. However it does not do that great a job on the several coats of shellac that are under that.
After testing several things, formbys, Liqui strip etc, the best thing I have found to actually dissolve the shellac is denatured alcohol applied with a steel wool pad. It seems to dissolve it enough to allow for removal.
The next step seems to be to take a palm sander (60 grit), and run it lightly over that which seems to set any leftovers.
One more light application of the citristrip after that and you are down to a clean floor.
But boy is this a lot of work!