[robespierre]

The hard drives are not encrypted, so there is no need to "break in" to anything. You can simply read what is on the disk and copy it to another volume if you want to do that.

80-pin drives only connect to backplanes. It should not be difficult to find them, here is just the first search result.
The backplane connects to your power and SCSI cables, not the drive.

If what you want to do is bypass the password so you can use the Octane with its existing system disk, there is no real security preventing that. Once you load the IRIX installer from a CDROM or the network, you can change the password from there.