OK so for the record, I just tried USB disk drive on another computer, installing the 3 drivers one by one, starting with the diskdrive driver, then the one right above it, then the one in the parent folder (after you unzip it all, naturally).
Conclusion: you need all 3 drivers for disk drive mode to even become an option.
Conclusion: you need all 3 drivers for disk drive mode to even become an option.