1966 Plymouth Barracuda Help!

ill have to take a look at my heads and see if they're cracked. The Positive and Negative both read 11-12v on the coil but read 5-6v at the end of the Coil wire that plugs into the distributor. Ill try messing with the timing. As for the Gauges a lot of them don't work. The temp "does" and the spedo works but nothing else. When the temp goes hot it stays hot until i release the pressure at the radiator and let it cool down.