Hi, I have been getting a lot of requests for this information so I thought
I would post it for those interested parties. (Sorry for length).

To increase the MacIISi speed to 25MHz or 33MHz the clock must be changed
from 40MHz to 50MHz or 64MHz respectively.
This is done by going to a static-free work station or putting some
aluminum foil down to work on.
	1. Open up the Si by lifting the tabs at the back of the case.
	2. Remove the Hard Disk by disconnecting the power and SCSI cables,
		spreading the tabs, and lifting the drive out.
	3. Remove the flopy drive.
	4. Remove the power supply by spreading the tab in front and lifting
		the supply straight up and out.
	5. Remove the fan by pressing the ears together at the back, bottom
		side of the fan and lifting straight up and out.
	6. Remove the Mother Board by spreading the tabs on the left and
		right side of the board and sliding the board forward then
		lifting the board out. (all connectors on the back of the
		board must be removed first)
	7. Desolder the 40MHz clock (the one closest to the memory modules).
		This is not easy even for a skilled solderer.
	8. Get an IC socket with the round pins and remove four of the pins
		by pushing them up from the bottom with long nose pliers.
	9. Put the four pins in the holes vacated by the clock and solder 
		them in.
	10.Insert a 50MHz or 64MHz clock.
	11.Put large power transistor heat sink's on the processor chip and 
		the other large chip just to the right of the processor and
		figure some way to hold the heat sync's in place. I made a
		simple clamp by putting a four inch screw up through the hole
		in the board between the two chips. Mount the screw using
		insulated washers. Screw a cross member down over the heat
		sync's to hold them in place. Don't use too much pressure.

	12. Put it all back together and go-for-it.

Disclaimer: this is only the procedure I used and is not authorized by anyone.
	    You are on your own for this procedure. I'm quite sure it will
	    void your warentee.