I stripped both screws before reading these comments- disaster.
The only reason for removing these screws is so you can get access to the Torx screw beneath the Bluetooth/wireless board (ie the top left screw circled red in step 9). I Had the idea of drilling directly into the black wireless/Bluetooth plastic board directly above this top left Torx screw shown in step 9. I could then use a long thin Torx screwdriver to reach through the hole and unscrew it, without having to remove the stripped screws holding the wireless/Bluetooth board in place at all. Be careful drilling into the board(!), but worked perfectly for me. Once the Torx screws are removed, it just takes a bit of jiggling to carefully remove the optical drive out from under the board, and put the hd drive in.
If you're reading this before having stripped the two screws, I'd recommend not even trying to unscrew the Bluetooth board and just drill a hole in it, assuming you have steady hands. I'll try to upload a photo to show what I mean.