Well, I just managed to replace the belt! I didn’t need to disassemble the drive or even remove it from my case. Just popped open the tray (manually, with the ejection hole, while powered off) and then used fingers and an awl to get it over the two spindles - the photo you posted really helped, thank you! I am always happy when I can fix something for a few bucks that would have taken close to $100 to replace (if I could even find one).
In case anyone else is reading, I found the belt at Turntable Needles, and the model I ended up using was the 4.0 inch square belt.