I have a system that kicks the IGNITION to 12 volts while leaving the rest of the car at 6 volts. This igintion boost only takes place when cranking. MORE INFO at 12voltseasy.com.

CORRECTION OF PREVIOUS POST. The site regarding the 6 volt to 12 volt IGNITION ONLY system is:

info@12voltseasy.com. Works ok, and eliminates changing bulbs, headlights, putting in resistors for the radio, heater or OD, etc.. The voltage boost goes to 12 volts only when cranking and reverts to 6 volts once the engine is started. the boost only goes to the ignition without changing the rest of the electrical system.

Years ago, I had a 1960, 12 volt Citroen. It was a great car, but it was very rusty. I then bought a non-rusty 1959 Citroen. It was an identical car except that it was Citroen's last year of 6 volt cars. the 12 volt car had always started right away, but the 6 volt car turned on the starter quite a while before it started.

I solved the problem by putting a 12 volt battery in the battery box. It is only connected to the starter ( I still have the car). Everything else remains 6 volts, including the ignition. the 6 volt battery is on the floor next to me. The car starts right away. I am using the original starter. If I'd had a 12 volt starter, I would have put it in. I have not had problems with the starter. I just charge the 12 volt battery occasionally (like a plug-in hybrid!)

People have commented that Hudson starters should be rewound for 12 volts. That would be good if anyone wants to use this modification.