The sidewalls combine what looks like a pair of doors with the crossbeam top structure seen with the arches.

Actually this is not quite true. To make a strong joint between the wall and the cross beam, I made the walls 3” taller than the doors, and screwed them firmly to the crossbeam. The decorative strips under the sign are thus 1 ½” narrower on the sides.

The picture above shows detail of how the walls are built up.

The walls themselves are made essentially the same way the back was done. The side edges were drilled to take furniture fasteners, and bolts driven through the arch protrusions to screw into them, thus joining the sidewalls to the arches.