I'll dig around and see if I can find those mod instructions - but here is the gist of it.
The bus frequency is not very safe to alter. Even though the RAM is rated for PC100, I discovered that the machine was very unreliable with a 100MHz FSB, regardless of the core speed. Sadly, that setting is the only one on the top side of the board. The clock multiplier is safe, but you will have to completely remove the mainboard from the chassis.
Now, look where the ZIF socket is on the bottom of the board, and you will notice R500, 501 and 502 (could be 501,502,503 - can't remember). Off to the side is a chart with those R values and multipliers. Pick your poison, and then rotate the resistors as needed. Unfortunately, the most common multiplier requires rotating all three resistors. The easiest way to do this is to use desoldering braid to clean off one of the contacts (the one you aren't rotating about) and then melt the solder and rotate the part with a toothpick. It isn't hard, but it does require a good deal of dexterity.
If you need, the core voltage is also on the bottom of the board, near the power supply connector. Likewise, there is a handy chart printed in the silkscreen.
