Russ, the autolite 46 is one of the least expensive plugs that you can purchase. I like NGK iridium WR51X, 7510, but they would be a waste of money in an oil burner.
I would go to the parts store & purchase an oil fouler adapter to space the plug out of the combustion chamber. I have used this type of adapter before when I couldn't afford to rebuild the engine.
If your fouling condition is mild, you can enlarge the flame travel hole where it exposed to the combustion chamber, also you may have to go to a colder plug since you are creating a longer heat path for the plug to run at the proper temperature.
Just use the adapter in the cylinders which foul plugs.
Have been down your road many years ago, you got to do what you got to do.William