Hinge? Just nail it to the top. ;)
You could always cut down a flat metal hinged tail piece (not the rod type that you've already got), so you could glue + screw the metal piece underneath the wood.
But as you are going for a tailpiece where the strings drop in from the top, then you don't really need a hinge as such (as you won't need to lift the tailpiece to help slot the strings through the holes), just a metal bracket bent to an appropriate angle.
In fact, looking around for a suitable example I came across this, which might give you some ideas:
http://www.victorbakerguitars.com/bl...tar-tailpiece/