Well, I went and bit the bullet. It doesn't work. I'm not 100% sure why, but I think it's just incompatible. The machine will hang at the "wait a moment..." message. Oddly enough, you can still play back the audio tracks using the front panel buttons.
The board on the inside looks slightly different, but other than that it looks totally identical to the normal TG-16 drive.
What IS different is the model number; the PC Engine's drive model is CDR-30A. I really should've done my homework here. The only silver lining in this case would be if the entire disc mechanism can probably be transplanted from this new drive to an old dead drive without any need to mess with the laser directly. I guess I should try that next.