Drop a plumb line to mark the center point of the column, and mark the point with a permanent marker. Measure for the height of the column from the floor to the ledge (Image 1). Measure the capital, base and 1/4" plywood cap (Image 2); subtract that number from the measurement made on the column.
Cut the column to the exact measurements previously calculated (Image 1). Attach the capital and base to the column with wood screws (Image 2). The base cap is 10" square. Measure 5" on each side of the original mark and mark with a permanent marker (Image 3).
Slide the column into place, using the marks on the floor as a guide. The column should fit snugly once in place. Add the plywood cap and secure the column with wood screws. Repeat the process for the second column. Make sure to fix scratches and do touch-ups to the painted walls as necessary.