https://www.heise.de/ratgeber/Mezzanine-in-neueren-iMacs-305998.html
Here is an article about retrofitting the molex connector to later models that don't have it because Apple noticed what was going on and didn't like it :-)
The article is from the best German Computer magazine, c't, Google...
Here are the pictures as proof that I wasn't kidding. The box in the back is called Power R video adapter.
There are three operating systems on the iMac: 8.6, 9.1.2 (?) and 10.4. I bought the iMac brand new in 1999.
Once lightning struck and the Ethernet port died as a consequence. I...
I also have a - literally - fully loaded rev. B iMac with the following:
Sonnet Harmoni G3 500 Mhz
iPro Raid TV SCSI TV tuner card
512 MB of RAM
Adapter to connect an external monitor (forgot the name of it).
By now it is 24 years old and I am still using it to scan with an Epson scanner...