FLYBOYJ
"THE GREAT GAZOO"
Allied aeroengine engineers regarded the germans somewhat lagging in spark plug or ignition consciousness and development. There is a book on this "the vital spark aero engine spark plug development" of course allied engine technology was extremely agressive on the spark plugs (rich mixtures and lack of fuel injection). The plug has to keep cool enough to prevent pre-ignition but also able to remain clear of fouling and create a potent spark.
overhead camshaft | pdf archive | piston-encine progress | 1945 | 2398 | Flight Archive
The engine is no heavier, maybe 15kg for the AS engine with the bigger supercharger.
Still doesn't explain what the swedes would have better spark plugs. Did they make their own? I doubt a western plug is going to fit into German engine...