Heres my thoughts. Any wiring will eat up lots of time,so I only want to do it once.
In 1940 they did not use fuses so none of the circuits are protected. So I would by a 20 circuit wiring kit so that you have circuits for any thing you want to add down the line,you can simply tuck unused wires behind a kick panel. Change all the bulbs to 12 volt,I would use a G.M. alternator,you will have to fab brackets for it.your 6 volt starter will work fine.Painless and others sell a converter that you can install to make your 6 volt gauges work.Swap the 6 volt ign.coil to a 12 volt and install a ballast resistor.All of your stock switches should work fine.