Since my cousin,  Margaret Gribbin found Henry's true origins in Jan 2023 by searching digitised German church records using  the Familysearch website and found Heinrich with a birth date 19th October 1845 and parents Lorentz and Margarethe Hammann.

The above details matched earlier information gained by Margaret's father and aunt albeit with surname Loehr. It was also believed that Henry's father was a school teacher. Margaret wrote to the Michelstatd Stadtarchiv and received a reply confirming "Lorentz Kussner(Kuessner)  was the Vielbrun schoolmaster and taught from 1830 to November 1874. Lorentz was born in Neustadt (probably near Breuberg) on  August 31, 1805. He married Anna Margaretha Hamann in Vielbrun on June 6, 1832. Lorenz and Anna Margaretha later moved to Braunshardt  (near Darmstadt)  to live with their son-in-law (Johannes Klein) on November 2, 1874. His wife Margaretha died on March 1, 1888 and Lorentz on February 28, 1888."

Margaret Gribbin found that

Heinrich was the 8th born of 11 children of whom 4 died in early childhood 3 before Heinrich and 1 after his birth. Three of his brothers preceded Heinrich's migration to the United States and settled in Ohio state. 

Henry worked as a boatman on the Mississippi river and signed up to the US brown water navy on August 11, 1864 and initially served o the USS Grampus.  He was dismissed from the navy on June 10, 1865 at Mound City Illinois.

Henry Kussner on Sep 15, 1865 at Buffalo NY enlisted in the 14th Regiment infantry Company D, 3rd  Batallion.  His physical features age and Germanic origin match the description on his naval enlistment record.

Henry deserted his unit on February 4, 1866 as detailed in a report to  army headquarters at the Presidio, San Francisco. It is currently thought he deserted at Fort Yuma, Arizona which borders SE California and Baja California, Mexico.

The remaining challengers are to find Henry's entry date to the US under the name Kussner,  I have two possibilities 

Neptun arr New York on May 13, 1859  ships manifest

Henry Kussner arr 1863   ref from Immigrants from Odenwald District of Hesse Book 2       author GEIG, Ella 1989 240p

Finding Henry's departure from the North American west coast under an alias is the real hurdle.