Nick, As jerry says the wire on the starter mounted switch, that is on the same stud as the battery cable, is how power is tapped into for varios reasons. Like if you added a wire to the battery post to supply power to something. Like Jerry said it is commonly the ammeter feed. In yout "start up wiring you ask for, that wire can be used to supply power to the temporary ign switch bat terminal as mentioned in my No.5 answer to your post 21Jan. Engine Shop post.
As said, for 12V you will need a 12V externally resisted coil. You seem to have that.
You need the side terminal switch Jerry and I linked 21Jan, you need a ballast resistor......I spelled this out and how to wire on your post in "Engine Shop". 21Jan. I realize you are mostly asking about distributor and starter now.
The gurus here say that the 6V starter will work on 12V. If it did not have side terminal, it's probably 6V.
If your distributor is wrong for 12V, I'm sure it is saleable here in the For Sale section. Folks here will have the correct one to sell or trade.
Keep asking questions.
