what is the procedure to eliminate and re-plumb the breather pipe from the rear of the valley cover into the base of the carb?
I'm assuming you are talking about installing "Positve Crankcase Ventalation" to replace the draft tube. Fundamentally remove the draft tube, install a PCV valve inline to the carb base vacumn port, clean the oil fill cap or install a newer one that has a line to the air cleaner and a filter there. You need to make sure there is a mechanism to return oil caught in the vapor to the crank case. This can be a simple wad of course stainless steel wool under the PCV valve contained in a basket that will contain the stainless and allow the oil it captures to drain out. Look for a PCV valve that comes from an egine of similar displacement.