Thanks Mijzelf for this clever solution. But, I did a test with a smaller capacity HDD and I still can't boot (No longer the GPT error message). I think I'm going to have to, as bodhi suggested, update my uboot. Once my uboot up to date and I am able to boot from a 500 GB HDD, I will try with my 6TBby Morbus - uBoot
I did not install the new u-boot because I have bads blocks in my NAND. I will double check and, if true, I will ask for help in the relevant thread. Thanksby Morbus - uBoot