Is my ‘56 truck 6V or 12V

[M37grunt]

As mentioned before, my new, to me, ‘56 truck has both 6V and 12V bulbs.
Already started conversion to 12V. Alternator, coil, condenser etc.
Headlights are 6V. Dash bulbs are 14.4V.
There has been talk of a 12V to 6V resistor.

My concern is avoiding damage to any of the gauges by running 12V to all.
Are resistors needed and which ones need to be protected.

Here are some pics. What’s the small rectangular device above the fuel gauge. Resistor?866D0195-6A71-47D6-AEBF-CD32779211D7.jpg