hard drive - how to recover a big NTFS partition that's missing the first 4kb?

I have two external USB3 HDD drives (2.5", both from Toshiba) that have a bad sector. One drive is sized 500GB, the other is 1TB. Interestingly, both show exactly the same problem:

The partition table is okay, but the drives are not able to read the very first 4kb of the single NTFS partition.

I was able to recover the rest of the drive using ddrescue, but - as said - the PBR is not recoverable.

the ddrescue map file looks like this for both drives:

# Rescue Logfile. Created by GNU ddrescue version 1.16
# Command line: ddrescue -s 1G /dev/sdg TEMP.img TEMP.img.map
# current_pos  current_status
0x00100C00     +
#      pos        size  status
0x00000000  0x00100000  +
0x00100000  0x00001000  -
0x00101000  ...         +

For reference, the partition table of the smaller drive:

# fdisk -l /dev/sdc
Disk /dev/sdc: 500.1 GB, 500107859968 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773164 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 identifier: 0x460692ac
   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1            2048   976769023   488383488    7  HPFS/NTFS/exFAT

AFAIK any NTFS partition should have a copy of the PBR somewhere, but I'm not able to read (mount) the partition neither with Linux, nor with Windows 7. They claim that the partition is not formatted.

Also tried with "Testdisk", but it is not able to restore the PBR as it can't find the root directory.

I'm experienced with parititioning (MSDOS, GPT) and linux file systems, but not that much with NTFS. Any way to recover that data?

The disks contain mainly photo files (Canon RAW, .CR2 format) and Adobe Lightroom catalogs.

Apparently the 500GB disk is actually formatted in FAT32, even if the partition table claims something else. I guess Windows doesn't really care the partition type and rather looks at the partition contents. When configuring Testdisk to expect a FAT32 LBA partition, then it is able to find the root directory and some subdirs (I think that proves that it's a FAT32 partition). However, Testdisk fails to find the vast majority of the files - no clue why.

As for the 1TB disk: Testdisk does not find any files neither in FAT32 nor in NTFS mode. I'm currently running RecuperaBit in hope that it is able to succeed.