The second article indicates that the barrel was cast in 1863 and acquired in 1868. I am not sure when the Tredegar Foundry was rebuilt after the war, but 1868 sounds a little too early.
A biographical note on Tredegar
http://vip.lib.virginia.edu:8080/cocoon/vivaead/published/lva/vi00494.bioghistBy the beginning of the Civil War, Tredegar was the largest ironworks in the Confederacy, with almost 700 black and white workers. The ironworks was virtually the sole source of heavy guns, projectiles, gun carriages, plates for iron-clad vessels, wheels and axles for railroad rolling stock, furnace machinery, and a variety of other products for Confederate munitions factories and navy yards. Although heavily damaged during the evacuation fire in April 1865, Tredegar made a swift transition back to peacetime production. The company was reorganized in 1867 as a new corporation, the Tredegar Company, whose assets were the Tredegar works, including the Armory rolling mill. Joseph R. Anderson and Company continued to hold interests in the remaining furnace properties.
In 1868 Tredegar received a major contract to supply the Chesapeake and Ohio Railroad with rails and bridgework for the entire line. A national sales office in New York City was established, with John Tanner dispatched to run it, and a network of agents were positioned across the country. Foundry, rolling mill, blacksmith, carpenter, and boiler shop facilities were expanded by 1869, and a new puddling mill was erected. The rail rolling facilities were upgraded and new chair mills, spike machines, and horseshoe machines were introduced. The company made some non-railroad products, including engines, boilers, cast-iron pipes, nails, marine plates, bar and angle iron, decorative iron building fronts, and structural bridge iron. By 1873 Tredegar had more than twice its prewar capacity and employment that exceeded its highest antebellum totals. During this period the company supplied iron bridges, rails, and thousands of kegs of spike which were used to rebuild southern railroads. The company survived the panic of 1873 but was forced into receivership in 1876 when several northern railroads with which it had contracts and agreements were forced into bankruptcy.
Field Artillery Weapons of the Civil War by James C. Hazlett, Edwin Olmstead, and M. Hume Parks (p. 144).
“There is no evidence that any Dahlgren boat howitzer was made in the Confederacy between 1861 and 1865, but one is known today made by Tredegar Foundry in 1868. Marked with the Great Seal of Maryland for the State Oyster Police Service, it is mounted for use as a field piece by a skirmish group.”
