You are almost finished. Reassemble the case and put the screws back on.

Print a label that clearly states that your drive now takes 12V DC center positive. Don't call this project finished without this step.

You want to avoid any confusion or someone plugging in an old AC power supply to this modified drive.

For DC, you can actually go higher in voltage, all the way to 15v, even 18v. The power section of the drive may heat up a bit, but it will work regardless, with minimal risk.

Still, you want to stick to DC, not AC so the label is a MUST.