It's a Norton, anything is possible!
If the bikes on it's sidestand, who's to know where the oil will get splashed!
Try less oil in the oil tank
My Commando used to do this.http://www.nortonmotors.de/ANIL/Norton% ... 13&Part=45
Breather on mine goes into the back of the airbox, Black smoke is carbon because it is running too rich and white smoke is oil.
Could be valve guides, could be piston rings, could be head gasket, but it's a Norton so check simple things first.