If it's reporting "1.58Ghz" speeds, it could be more the motherboard misreporting the speed, which can be tweaked with entering various commands into Open Firmware. Not all Macs of this era do, but of note iBooks do the same thing.

The "resistors" used for setting a multiplier are just 0K shorts, you can check for continuity. If not working, you can safely remove the resistor and use a piece of wire, solder, or conductive ink to replicate this.

JB