There's a guide to IDE SCSI adapters here
With the Apple 1GB + ADTX PB SCSI drive, you can replace the drive with any 12.5mm or thinner IDE drive. However my ADTX adapters can recognize only a max of ~8GB /
Upsizing an Apple OEM 1GB drive
I formatted an IBM 10GB Travelstar / on an ATA-bus equipped PB, then transfered it to the ADTX adapter plate. At first glance the drive appeared to be all 10 GBs but testing revealed an unholy mess of read-write errors.
Upon re-initializing the drive (using Drive Setup IIRC) it then showed up as an 8.x GB drive with the remaining portion not visible or available for use. Worked fine though, and was quite a bit faster than the old IBM 1 GB dog with which the adapter originally came.