You need to replace the last 64KiB with “art” block (contains radio calibration data), AND you need to replace the second 64KiB with the corresponding data block of the original flash (it contains MAC address, device identification code, and PIN if applicable).
You should be able to assemble flash image yourself.
The parts you need:
1. U-boot. That’s the first 64KiB block of the original flash, or an alternative uboot from pepe2k, namely uboot_for_tp-link_tl-wr703n.bin from here. Whichever you choose, I’ll call it uboot.bin in the following (exactly 65536 bytes).
2. The second 64KiB block of the original flash. I’ll call it data.bin in the following.
3. OpenWRT Attitude Adjustment image for your device, get it here. I shall call it factory.bin in the following.
4. Optionally, create a file empty.bin which is 12648448 bytes in size and contains FF’s (actually, it may contain anything, it shouldn’t matter).
5. The last 64KiB of the original flash, I’ll call it art.bin in the following.
Now, combine the parts into the final image.bin. On Windows, it would be
copy /b uboot.bin+data.bin+factory.bin+empty.bin+art.bin image.bin
(On linux, you do it similarly with the “cat” command.) The resulting image.bin should be exactly 16MiB, the size of your flash.
Alternatively, use your hex editor to create an empty image.bin with the size of 16MiB (16777216 bytes), then paste into it (overwrite bytes, NOT insert)
1. uboot.bin at file offset 0;
2. data.bin at 0x10000;
3. factory.bin at 0x20000;
4. art.bin at 0xFF0000.