I can second what Gil and LCGuy have written. The plastic HDD sled used by Apple for IDE (as they were, so long ago) was/is different in detail from that for SCSI HDDs. It has a narrower 'tongue', and is easier to break if you rely simply on brute force for its withdrawal. Use the long-nose pliers on the tongue to lift it, and wiggle the sled from side to side. Even if you feel no perceptible movement you may succeed in loosening the bonds of affection between the sled and its rails. Then, keeping the tongue raised so that its pawl clears the retaining slot, draw the sled out with a sustained pull rather than a sudden jerk. You'll succeed in the end.
de