It's not the question you asked but please allow me to ask you one. Why do you want to convert to 12V?
First of all, it's your car and you're free to modify or restore it any way you want to. Personally, I welcome suggestions but really dislike people TELLING me what I should do with MY car.
Are there some 12v accessories you want to run or are you just not ecstatic about 6V starting? Perhaps there's something you're not satisfied with that a 12V won't correct. Potentially you'd cover up a problem that's better fixed another way.
I bought my mostly original '41 about a year ago and had lots of plans for upgrades and modifications. I took some advice to slow down and get it running perfect in stock configuration before making modifications. For the most part I've done that and glad I did. It's nearly always more economical to make an original work right and if you it getting working right you might lose interest in the modification. Also, the more you modify an original, the more you're on your own. No one else has a car just like yours and once you modify one thing you're forced to adapt to your modification and then you're forced to adapt to your adaptations etc.
A 12v conversion was going to be my first project. I took the "slow down" advice, held off, and still have the 6 volt system. I now take a great deal of pride in making it work right.
Again, it's your car. I'm not telling you what to do with it. I'm just asking a question and suggesting that keeping 6 volt MIGHT be a good alternative. If you reply with your motivations for a 12 volt conversion, it's possible you'll get some good alternative suggestions.
Modified cars are lots of fun too.
Best wishes with your conversion!
