Yes, you can use any 50-pin drive, of any byte-size. You simply have to note that System 6.x can only see up to 2GB on hard drives. But since 80MB < 2GB you can certainly use your drive with any OS your Mac supports.
The only thing you have to watch is TERMINATION. You can often terminate newer SCSI drives using a jumper on the drive itself. Older drives don't offer that, so you will need to use an external SCSI terminator. If you don't terminate the drive, it won't work at all or won't work reliably. And this goes without saying but I'll say it anyway. If you terminate the drive using a jumper on the drive itself, you do not need any terminator on the external SCSI port of the HD20SC. Just terminate it once (either internally or externally).
The only thing you have to watch is TERMINATION. You can often terminate newer SCSI drives using a jumper on the drive itself. Older drives don't offer that, so you will need to use an external SCSI terminator. If you don't terminate the drive, it won't work at all or won't work reliably. And this goes without saying but I'll say it anyway. If you terminate the drive using a jumper on the drive itself, you do not need any terminator on the external SCSI port of the HD20SC. Just terminate it once (either internally or externally).