RE: if your glow engine was in your car
Yes you are correct in that Renault had serious QC problems and along with failing to meet emissions regulations, they gave up the US market.
Fiat, on the other hand, ran afoul of US terrorism laws when Khadafi, the ruler of Libya, bailed out the failing company and bought a large shareholder interest in the company too. Libya was a terrorist state at the time. So Fiat wound up banned in the US at the time.
On the old leaded gasoline engines. You normally would get a set of new valves (mainly the exhaust valves) so that the valves could handle the higher heat range of unleaded fuel. Otherwise the valves would burn out fairly fast. You also may have had to lower the compression ratio if the engine was running a high compression as well. I don't remember anyone putting in valve seats as well, but it has been many years since I messed with them though.
A engine burning alcohol would more easily pass emissions standards as alcohol is a much more clean burning fuel than gasoline. If I remember correctly, it wouldn't need a catalytic converter either. I'll have to study that more though.