I had all the C67 series and I still have a couple of images of the original firmware, but I don't remember which model they belonged to. Here are the links in case they might be useful for you.
https://drive.google.com/file/d/1KdL...w?usp=drivesdk
https://drive.google.com/file/d/1oZP...w?usp=drivesdk