I know this is a stretch but I had a similar issue with an old DB walk behind that belonged to my grandfather. It lost its spark and he couldn't figure out why so he repowered it. Fast forward 15 yrs and I had the original Briggs motor on the bench and was troubleshooting it. I had he engine tins off to get to the ignition and turned it over with a drill on the crank. The lighting in the garage wasn't the best which was a good thing. I noticed that the coil was arcing to the block. The insulation on the coil wasn't the best and it was shorting out. I slapped some silicone sealant on it and the damn thing fired right up.
Point is, look everywhere when it comes to ignitions, you never know where they might fail.