Your not weird. You are here right?
This the precursor to the Smart Car. (The uncar).
Conversion to 12 volt is the correct way to go. Voltage reducers are common for whatever needs to remain 6 volt. Speedway Motors - Street Rod Parts, Race Parts, Ford Flathead Parts, Sprint and Midget Racing Parts, Pedal Car Parts
On the American cars that have been converted to 12 volt the 6 volt starter works ok on 12 volts.
The other option is a dual voltage system that uses (2) 6 volt batteries in series. A 12 volt alternator will be required and many common alternators can be adapted.
Also a separate fuse block will be required for the 12 volt loads.
While your at it why not drop an SBC in it?