[Jordan Baker]

The holes are just holes. No threads. In the factory photos there were a pair of brackets on the front box panel with what appears to be stops on either end.

The factory photos are of an earlier box, the C series, whereas the production ones were the later 2J3's There seems to be some slight differences in the box its self.

I believe it was Brian Asbury who told me that the Wire-3 truck he had at one point had clips mounted under the box or on the frame for holding an antenna mast.