Hi Bruce
I've seen the solution to this problem listed on some of the HOTROD Chevy Stove bolt 6 sites. If I remember correctly the solution is a dropping resistor which supplies 6 volts to the instruments temperature sensor, oil pressure and gas gage. Changing the early 50s Chevys over to 12 volts when hotroding the engine or replacing with a V8 was very common.
Try a google search on "6 to 12 volt conversion chevy"
http://www.google.com/search?hl=en&q...=Google+Search you should get a number of good write ups. I saw a number of sources for the conversion resistor.
I have a friend that converts all of his CCKWs to 12 volt and he uses the dropping resistor to convert the gages. I'll ask him what resistor he uses.
Cheers Phil