I had not heard of this land grant. Do you have a copy of it? I show that he was married in Mississippi in 1839. I may have errors, however.
The Hallmarks were also my great great grandparents.
How does your line go?
I would be interested to learn more about the document you mention. My email is firstname.lastname@example.org
if you would like to email directly. I also have a picture of them, if you would like one.