I think i found the answer with the tach. There is a special plug with two wires. One for the one wire system, the other for the tach. The one I found is NEW HEI Distributor Wire Harness Pigtail Dual 12v Power and Tach Connectors 170072. Will that work?
I also found an ignition wire set: HEI Spark Plug Wire Set for 1941-1962 Chevy Chevrolet Inline 6 194 216 235 Oem Fit PWJ132. This sounds like it might be right for the HEI dizzy.
This is a one wire system. Does that wire go to the ignition switch?