Coolio, if for resale understandable. Personal taste really. I wouldn't consider putting a drive back on a hard card as they get way to hot to be hanging around on a piece of pcb. In essence thats why they disappeared from hard cards in the real world, as the failure rate was massive. Good case mount or even external case would be preferable for reliable operation.
If heat is a real issue with hard-cards, you could probably make a little space between the drive and the card (for air circulation beneath) by using standoff bolts like this:
They have a female threaded hole in the top you can't see. So these brass standoffs screw into the harddrive, then harddrive is positioned on the card and the heads of these standoffs lined up with the bolt holes in the hardcard, then the bolts normally used to mount the harddrive to the hardcard go into the heads of these standoffs.
