Found a mention of J. G. Langston -- in a friend's collection of newspaper clippings he generously shared:

"Veteran Jessie Grimes Langston, October 27th, 1913, Age – 66, Mattson, Mississippi, General Debility. Mr. Langston died of Apoplexy, January 17th, 1914, Sick only a short time – was buried in the Confederate Cemetery – Mr. Hillhouse officiating,. Mrs. Nancy Gordon, Banks & Kaufman attending, his nephew & sister were telegraphed of his death by the President of the Order. – With no expense. – Later a letter came – Expressing much regret that the Sister’s illness prevented her coming & great gratitude given to the Order for their kindness to Mr. Langston – Her letter w
as full of love & praise for her brother’s Christian life - That he had been a sufferer so long."

and

"Deaths; Veteran J G Langston died January 17th, 1914."

The date Oct 27, 1913, above was when J. G. Langston entered the Hospital Annex in Vicksburg. The Annex was built by the UDC specifically to care for old CSA soldiers who needed extra help.

Still haven't been able to verify his regiment.