Avgas can have Lead in it. Some doesn't. Needless to say Jet fuel wouldn't work.
Lead won't hurt your motor BUT if you have either a catalytic converter or Fuel injection with an O2 sensor you don't want to use leaded fuel.
To our French friend I'd say some
oil company's use Toulene or Xylene to up the octane on their fuel. IF you mix it at no more than 20% you won't have a problem. I and many others have used it for years. I don't think any one on this board wants to hurt their engines as they are ALL expensive.
Oh, and if your compression is low enough you don't need any boosters. They won't increase power in an engine that runs fine on normal pump gas. IMO, of course...
Regards,