It's been literally a decade since I had a 5xx, so take this with a grain of salt, but I recall most contemporary SCSI drives fitting the little card-edge adaptor thingy. Seems like I had a 2GB drive in one.

The fog of time obscures, but 50 pin SCSI drives don't have a lot of leeway for different configurations. As long as there's only the one thin plastic divider between the 50 pins and the power plug, the adaptor should fit.