Re: Exterior toe kick
I'd say not a good idea. Stone in that location is going to trap moisture against the sill. We already see that it is a damp location since the first piece of wood rotted out. The best plan would to properly flash against the sill, then replace the wood sub-threshold with a better quality piece of wood, with spacers behind it to maintain an airspace so it would not stay wet. wood/wood sandwiches are doomed, and putting masonry (stone, concrete, brick) directly against the sill is not advised unless some moisture barrier is introduced. The suggested screws or bolts are going to penetrate the flashing and give an ingress to water.
Remove not the ancient landmark, which your fathers have set.