This was a Christmas present I received from my wife. She thoughtfully bought it from Patrick Leach's December 2006 tool list (after a strong hint from me). Here's Patrick's description:
  MI49 Wooden pattern for a chariot plane; cast your own, in
       iron, steel, gunmetal, or solid gold, it's 6 3/8" long,
       and is in fine shape; would cost an arm and a leg to
       have made, it has a nice shape to it;
I'll add a picture of a casting when I produce one!