This is a metal tow bar, it is the same type as seen on Diamond-T wrecker trucks.
See this link:
http://www.g503.com/forums/viewtopic.php?p=748389&sid=3e674a2c090dcdefa23399eca12784bf
You can see the tow bar stowed above the rear wheels. On the M32B1 it was towed on it's side.
HTH
Marwin