[Lynn Eades]

Rob L., I think the mount is a one piece rubber mount that is probably captive in the cross member and held there with another plate on the bottom (I'm not sure about this particular set up) There are two steel bosses moulded into the rubber that stick up through the holes. The cast bracket bolts to these. The park brake anchor and speedo drive boss are part of the mount and can be easily seen.
I have one of those rubber mounts. It is a standard commercial Ford part, that used in conjunction with a std commercial cast mount, bolted to the back of the box at the holes you speak of. The LP2/ LP2A carriers used a longer rubber mount and a taller cast mount, both of which are Ford parts, special to the Australian pattern carriers.

Leo, I like your clever way of having only the front of the truck in your shed.