[leegreen]

I suspect you will spend as much on a step down converter large enough to run the rad fan then getting a 12V rad fan will cost.

based on past experience with this years back here is what I remember:

6V starter will be Ok if it is good shape and your engine fires easy, it is going to try to spin faster so it works harder.

6V generator with a 12v regulator was never very satisfactory, it wont start charging until 1500-2000 RPM. But a 12v generator from a 235 six will bolt right up

6v horn, open them up and clean the points just like you would in a distributor. Put a relay in and rock them on 12V they are LOUD. Just don't lean on the horn for a long continuous blast.

heater fan needs a big ballast resistor or a replacement

replace all the lights

if you have turn signals you will need a 12v flasher

you said you need new gauges anyway, if the old were any good:
temp and oil will work, they are mechanical
fuel level needs a ballast resistor
disconnect the ammeter, ignore it and add a volt meter. Safer and more useful

switches and wires will be fine on 12v if they are in good shape, but I suspect your going to want to replace a lot of wire.