Alas, I’ve got “the beast” iMac 1.25 20” FP that (so far) can only run OS 9 in Classic mode.
Fairly simple to disassemble and I just placed the screen face down on a towel before taking it apart for a good internal cleaning / dust removal. Eventually (and I highly recommend) I’ll also install an SSD. And an SSD will render that internal fan less necessary and prolong life. Biggest advice I’ll offer is to clean and renew all heatsink paste while you’ve got it apart.
You might also take a close look at any visible capacitors while you’ve it apart, looking for domes that have swelled and/or otherwise slightly or fully leaking capacitors.
As for the CD/DVD drive, you can sometime(s) “hook” a corner of the tray and carefully pull it out (while not plugged in / powered). Just enough to be able to get your finger on it to open the rest of the way. BUT, given the many foreign objects that I have found in such drives, it is a matter of “very careful feel” when attempting this because of all the possible obstructions. (i.e. jelly beans, hairclips, coins, etc.).
Perhaps you can post some close-up pics of its’ internals, once you get it open?
Best of luck and have fun!