But then we hit the first problem: the floor drain would not work properly with the planned new shower base! A properly built shower base contains a PVC liner that seals the shower area and directs water to the drain. There was no way to secure the liner to the older floor drain. A new drain was needed, which meant digging into the concrete. Scary!
To fix the drain we got the assistance of a professional plumber. Since he was already there we had him also dig up the toilet drain and move it further away from the wall. This lets us do a nice finished back wall, previously the toilet was right up against the concrete brick wall.