It's a simple enough procedure to carefully grind the top off a road draft tube, clean it thoroughly, repack it with coarse steel wool, and weld the top back on. In case the original top is damaged, just replace it with a proper-sized freeze plug and weld or braze it in place.
The road draft tube develops a vacuum at the tapered end of the pipe when the road speed is above 30 MPH. This draws air in through the slots in the valve cover, and ventilates the crankcase by pulling air down past the pushrods, and out through the road draft tube. It definitely needs to be free-flowing.
Jerry
