I did a flush on the Iron Maiden too a month or so ago. As Michael said that bolt by the oil pressure relieve valve is the easiest way to go. I loosened mine from the wheel well with a 12mm socket on a swivel ( looks like a universal joint) and 2 long extensions connected to the ratchet.... easy as pie !!
6 bottles GOOD QUALITY ( or Nissan ) antifreeze/coolant and 8L water ( total took 14L)..... yip I got a moooooorse big radiator in the Maiden !!
