You might want to look into an electronic regulator. they are not to tough to wire for gauges and small stuff BUT anything with high current loads will need more brute force i.e. BIG resistors.
I'll look in my curcuits and see what I have for a 12 to 6 volt regulator. One thing if you use and electronic regulator your voltage will be very stable, the resistor curcuit will fluxuate with the input voltage. There is also a thing called a Voltage divider circuit that is a little more complicated to wire for each gauge but it will work too. If your interested I'll calculate one up