I solved this in a ham-fisted sort of way. I put a 2x Toshiba XM-3401TA caddy-load drive in instead. It is working with the Mac OS 7.6 "universal" CD ROM driver. It took some hacking up of the Toshiba drive to connect to the CD SC's eject button, LEDs, audio outputs, etc but the original CD SC case is untouched so if I ever do get a working Sony drive to put in, nothing will be out of place. Most importantly, it looks entirely original from the exterior.