The road draft tube was fitted to allow blowby gasses to exit.
On early Falcons it was fitted to the front lft side fo the block and is roughly 1" in diameter. The tube extended downward and ended in a slant cut. The slanted cut caused a very slight suction effect as air passed by it, hence "road draft". On the valve cover a breather is fitted to allow air to enter the block.
The road draft tube was suplanted by the PCV system in the early sixties, although provisions for the road draft tube remained on subsequent later block castings, probably partly to allow for a casting core and partly to allow retrofit to earlier cars.
The PCV is a far better system.
