[[ leaving the original topic to discuss car conversions ]]
@ vee-tail 1 : I agree it is a scary idea to have the ignition depending on the electrical circuit - but is that not the case for a FADEC petrol engine too?
As for the French relying on French car engines: they do, to a certain degree, especially for the diesel. But in Holland, there is a project much like the Gazaile - I actually think it is based upon it - using a (heavily modified?) diesel from an Opel.
For myself I can't stop dreaming of converting the Subaru boxer diesel for aviation use - it is rated at 150 HP for road use, so should be able to power a 4-seater, perhaps not even needing a reduction. But the fact that no-one has yet done this seems to indicate the engine is not really a strong candidate. I wonder why, though.