Your 460 sounds like the oil rings are failing, allowing too much oil into the combustion chamber. This could cause carbon to build up on the piston crown, creating hot spots, and therefore preignition like you describe. Try running some of that Ford carbon remover through the engine. It works great! You will probably see black smoke for a while until it clears, and you may even go through a few cans... The carbon may have built up enough to crush the spark plug electrode. Also, valve stem seals may be dried up, and introducing oil into the combustion chamber, so that might be the first place to look, since it's the easiest?
I have had my share of oil burners, and almost all of them were 351M or 400. My 460 doesn't use any... And it is an original 1976 piece with who- knows how many miles...
Mark