How can I mount an old hard drive from SCO Unix in Linux?

My boss needs some files from an old hard drive. We have it connected with a PATA to USB adapter.

dmesg
[1568641.572757] sd 4:0:0:0: [sdc] 12594960 512-byte logical blocks: (6.44 GB/6.00 GiB)
[1568641.573263] sd 4:0:0:0: [sdc] Write Protect is off
[1568641.573272] sd 4:0:0:0: [sdc] Mode Sense: 00 38 00 00
[1568641.574935] sd 4:0:0:0: [sdc] Asking for cache data failed
[1568641.574946] sd 4:0:0:0: [sdc] Assuming drive cache: write through
[1568641.654625] sd 4:0:0:0: [sdc] Attached SCSI disk

fdisk -l

Disk /dev/sdc: 6448 MB, 6448619520 bytes, 12594960 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x44c21828

I copied the whole drive with dd to /var/tmp/scodisk. I ran strings and extracted a large text file which has much of what he needs but it is hard to use.

The sysv filesystem support was removed so I found and compiled an HTFS driver.

sudo mount -t fuse ./htfs /mnt/scodisk
    mount: /home/wsd/htfs-0.1.1/src/htfs on /mnt/scodisk type fuse.htfs (rw,relatime,user_id=0,group_id=0)

sudo mount -t fuse ./htfs --source /dev/sdc --target /mnt/scodisk
    /bin/sh: /dev/sdc: Permission denied

sudo mount -t fuse ./htfs --source /var/tmp/scodisk --target /mnt/scodisk
    /bin/sh: /var/tmp/scodisk: Permission denied

cd /usr/sbin ln -s /home/wsd/htfs-0.1.1/src/htfs mount.htfs

lsblk --fs (no UUIDs on the sdc line)

sudo mount -t fuse ./htfs /dev/sdc (sdc disappears from fdisk -l)

What am I missing?