Physically, will not fit unless you start cutting metal. Remove all electronics, including motherboard and PSU before chewing up the case, vacuum and wipe it out after.
Signal-wise, you can buy a motherboard slot card that has drive controllers on it, and connectors for the signal lines (SATA or PATA). Power cables have to be split with adapters that you buy. But do that only if your PSU has the capacity for all devices.
Highly recommended that HDD units be FIRMLY FASTENED to the case, not just set in. Any vibrations of the spinning platters must be dampened out. It prevents head crashes and data loss.