Is there any way the 2 pickup wires from the distributor could be reversed? If you are using the factory 73 wiring harness and nothing has changed at the distributor side (double-bullet connector) or the ECU side (big 5-pin connector), it should be correct. I know that when people wire their own, like to a GM HEI module, they often get the pickup wires reversed and then the timing is erratic, and the spark fires when the pickup is between reluctor teeth, not aligned with one.