so whats the alternative if you have a bad wire?The SOHC 450's have the wires incorporated into the coil, not replaceable. That's ok since the are a metal core wire and unlike the common graphite they virtually never fail. You can check the secondary resistance of the coil bu using a probe in each wire with a VOM set to ohms. Spec is 7.2K to 8.8K ohms.
I would replace the plug end caps since they're probably original, NGK part # XD05F. They are 5K ohm resistance pieces