[JayJay]

Marshall: the bows are 1" thick, and the mounting plate is 3/4" plywood. The plate is screwed into the bows from the back (I felt the screws), but unless you have the metal skin off your wood frame I don't see how that can be accomplished. I would probably fashion some mounting brackets from sheet metal and screw them into the faces of the bows and the mounting plate.

Attached are a side view picture of the mounting plate, and dimensioned drawings for you. The notch on the right (passenger) side of the opening fits the sloped bulb bracket housing, you'll need to fiddle with that to fit your lamp.

If you decide to use solid wood I would advise against pine. Pine does not hold wood screws too well. I'd suggest a stable hardwood like birch or maple.