I don't beleive the B F Lowe in the 3rd Tex Cav or Mann's Regt is the right one, he was about 20 years older that the tombstone birth date, age 41 in 1864.
B F Lowe with the right birth date, is in the 1860 Decatur Co., Tenn. census, more that likely came to Texas after the war.
Mike