Bill Doll's HO scale Forest Park Southern

In the article associated with this layout in the latest addition of MR, there is an incerpt dsecribing his valance. How does Bill attach the 1 X 4s and plywood base he used for his light fixtures to his drop ceiling?

I just read through the sidebar about the lights and I can’t find any mention of how he attached the 1x4s and plywood either. Maybe a communication with the editor via customer service can get you the answer.

Joe