Note: I purchased a new lower case 922-8285 and it included the hard drive connector.
You must have a magnetized Torx 10, 2 to 3 inches in length to safely get these screws out. Fortunately if you have the T10 you can magnetize it with your iMac.
Inside the front bezel are two magnets that hold your apple remote to the case, simply tap the T10 to the larger magnet 3 or 4 times and test it's strength in holding a weighty screw. You are good to go. I did this and the scary lose a screw into the iMac was diminished with a firm hold in both removal and install.