My apologies for a 10 day late reply. Mostly work, very little internet.
The only thing can offer is that for the 30 plus years I had a 1971 SA200 every time it would not run, other than drying out the distributer after a very damp night, it was the magneto. I've had it where I could see a spark (with a plug pulled and touching the engine) and it not start. New or rebuilt mag, fires right up.
The BEST thing I ever did was install a Pertronix electronic ignition. Same with my old 8N Ford tractor. Starts every time.
Someone with more knowledge of magnetos will have to suggest any trouble shooting or fixes.
I still have the 1948 Ford, not the Lincoln.
Floyd