Don't quote me on this, but I vaguely recall that if you want to replace the weird proprietary drive in the slot-loading iMac G3s with a more normal laptop one (like the PATA slotloading drives used in the PowerBook G4s) you can just take one of these things:
http://www.pccables.com/00507.html?gclid=CjwKEAjwhbCrBRCO7-e7vuXqiT4SJAB2B5u7MKiY7IqvfIDgDixgt3Ad8PCVmnC0qTSxKeu1eBAxlBoCy4bw_wcB
Break off the plastic around the connector pins (or find one without that plastic), and plug it into 40 of the 50 pins of the original drive connector that line up with the PATA hard drive connector. (Another alternative is to take a normal 40 pin IDE connector, trim the key tab off and file down one edge, and jam it into the appropriate 40 pins on the motherboard connector, thereby replacing the original cable.)
The thing you'll lose doing this is the ability to play audio CDs the "old fashioned way", IE, instructing the CD drive to play the CD with the built-in DAC and routing the audio through the analog pins; said pins are amongst the 10 extra on the proprietary 50 pin connector. If you can find a pinout of that part (Google's probably your friend here if you try hard enough) you could route those, but maybe you don't care. (It only matters if you use an old Classic OS CD player app or play an old-fashioned game that has redbook audio on the disk instead of fully digitized sound samples.)
http://www.pccables.com/00507.html?gclid=CjwKEAjwhbCrBRCO7-e7vuXqiT4SJAB2B5u7MKiY7IqvfIDgDixgt3Ad8PCVmnC0qTSxKeu1eBAxlBoCy4bw_wcB
Break off the plastic around the connector pins (or find one without that plastic), and plug it into 40 of the 50 pins of the original drive connector that line up with the PATA hard drive connector. (Another alternative is to take a normal 40 pin IDE connector, trim the key tab off and file down one edge, and jam it into the appropriate 40 pins on the motherboard connector, thereby replacing the original cable.)
The thing you'll lose doing this is the ability to play audio CDs the "old fashioned way", IE, instructing the CD drive to play the CD with the built-in DAC and routing the audio through the analog pins; said pins are amongst the 10 extra on the proprietary 50 pin connector. If you can find a pinout of that part (Google's probably your friend here if you try hard enough) you could route those, but maybe you don't care. (It only matters if you use an old Classic OS CD player app or play an old-fashioned game that has redbook audio on the disk instead of fully digitized sound samples.)