I've got several of the Acard 68 pin SCSI-ide adapters. I lucked out and found them in some old Macs I salvaged a few years ago. They work well, too well. A 7200 rpm 40gb ide drive connected to an Adaptec 2940 card outperformed a 10,000 rpm 36gb Seagate Cheetah.

One thing is that they add almost half an inch to the height of the drive. Though I guess you could take the circuitboard off the adapter plate and mount it somewhere nearby. I've used them with 50 pin adapters without issue.