Good question Rick. Wished he had a "how to" to see exactly what he had to do to make this work (assuming it is legit). See more below from sale site:
This is definitely legit, I'm the guy who preformed the modification :) (I'm not the guy selling it though)
The way this modification works is pretty simple, you remove the PPC750 from the iBook and solder a PPC7410 in. As the two are pin compatible it works "out of the box" (some jumpers also need to be moved around to set the CPU speed)
Some more info can be found here: https://68kmla.org/forums/index.php?/topic/28556-imac-g3-rev-a-c-g4... - as the title of that thread suggests I originally started doing this with a trayloading iMac G3. There aren't any pictures of the clamshell mod being preformed on there (there are a few of me testing the iBook though) but the process used on the iMac is exactly the same as the iBook though (only i'm using a much more expensive hot air station now :) )
That's freakin' amazing!