The boot boards are easy, poke em with your finger, if its kinda squishy its the FR one, if its hard, it the more performance/race version.
As far as the flex stiffeners, they get put into the spine of the boot on the INSIDE of the shell. You have to pull the liner out to do so. You can put two in each boot. Experiment with putting just one stiffener in either the top of bottom slot.