I had to scour the net and the forum. The 520 - 550c uses SCSI hard drives. This I have to apologize for. Sorry for the screw up.
But here is the basis of that screw up, there are a couple of old posts of members using the Aztec CF Monster Laptop SCSI Adapter to use a CF in a powerbook. CFs are IDE in nature.
I've seen these adapters on Ebay go for $120 or so from a couple of Japanese sellers.
