LR, here are some things you should note:
- HDD chips get very warm, this is normal
- Unless you are in a cleanroom and know exactly what to do, opening a HDD will render it permanently useless
- As boguing says, you need to find a drive controller board with a very close serial number - but if the drive is less than a few years old, even that may not work, as individual drive controllers are now calibrated for the drive in question during manufacturing.
But really I have little sympathy, because as mixture says, you should have backed this stuff up.