ratiocination

The hard drive can be removed with its bumpers intact, by just taking off the black plastic clamp to its right. Reinserting the drive is also vastly easier when done this way.

You're doing something wrong—only the left screw at that position needs to be removed to detach the heatsink from the logic board. In fact this whole walkthru would be simplified a great deal if it concentrated on removing the logic board, heat sink, and internal frame as a unit. There would be only 9 screws instead of ~25, and fewer chances to bend or break intricate parts.

It plugs into the logic board on the top side (opposite from the side showing in the picture) beside the FireWire jack.