1. Get two IKEA Molger shelving units.
2. Cut both according to need.
3. Drill holes to align vertical posts with wood plugs (I first failed to center perfectly, but extra holes and nails made alignment easy again).
3.5 (optional) cut an extra piece of wood for book support.
4. Pre-align, apply glue and plugs, hammer into place. Use spare wood to protect soft wood.
5. Done: Two Molgers turned into one extra tall and two shorter. Molger & sons.