If you use the drawing I posted above with the 7806 reg that I suggested you will get exactly what toomany2count posted from the HAMB site, except for the heat sink, which probably won't be needed with the current draw of the gauge (though the heat sink is cheap if you want to add it). If you use the drawing I posted with the 7805 reg and lift the ground with 1k potentiometer (trim pot), you will get an adjustable regulator capable of dialing exactly 6.7 volts.

I used electrolytic capacitors as they are a little less temperamental than the tantalums, but either will work and the tantalums are smaller (just be careful with the soldering heat on tantalum caps).

Each regulator circuit is about a buck ($1.00) to build if you use the source I provided or others like it, Radio Shack will be 3 times or more. Some of the online sites have a minimum, if you are building several regulators for multiple gauges it should put you over most minimum limits. If not let me know and I can get them for you on one of my next orders, I buy in bulk so minimums are seldom a problem (I may have 7805 regs in stock, used to use a lot of them).