Interesting rehab project. Our mission was to remove the existing steps and replace with natural stone risers and bluestone treads. Another challenge was to make sure the railing would go back on top of the new tread surface with no additional tweaking to the existing railing.
The infrastructure of the steps includes a base that was dug out, geo-textile fabric installed with a reinforced concrete base poured to facilitate our steps not moving. This is upstate New York, after all :)
We also removed the top concrete landing and replaced with pattern bluestone.