The problem with machines such as the LC/Performa 550 and 575 is that they used a cardedge-ish adapter plugged into the HDD. There is simply no room for any adapters at all or anything with it's connector in non-stock location unless you tear into the wiring harness.

You would be better off ditching the internal drive imo and using an external enclosure or something if you needed drives with adapters and whatnot.