Devildog,
It sounds like your problem is simply overfilling the oil tank. Before checking the oil always run the bike for 5-10 minutes to return any oil from the sump. Keep the level on the dipstick BELOW the "H" mark. I always shoot for the midpoint.
Most Nortons will wet sump if left for two weeks or more. Some more than others. This typically does no harm. In your case, it filled the crankcase above the camshaft and leaked out the camshaft/timing cover seal. Without overfilling the oil tank, I doubt it would normally reach this level. If it continues to be a problem, the timing cover should be removed and the oil pump serviced by disassembling and dressing all surfaces to insure a tight fit. A new gasket behind the pump and a new spigot seal would also be in order at this time. Then I would replace the seal in the timing cover and be sure to use a guide when replacing the cover. Finally a new timing cover gasket should be used. This should take care of problem, however, on long periods of storage it will likely still drain some oil to the sump.
The scavenge side of the pump is significantly larger than the feed side, so running the bike with oil in the sump will simply return it to the tank within a few minutes. However, if the tank appears completely empty, drain the sump before starting the engine and refill the tank. Do NOT start an engine if the oil tank is completely empty as the bearings will not receive oil until the scavenge side can start returning oil to the tank.