You're welcome - the four Custer Scouts on the Black Hills Expedition are:
Will "Medicine Bill" Comstock, chief of scouts. - either this is wrong or the picture is from an earlier expedition/campaign (Washita perhaps?)since Comstock was killed in August of 1868
Ed Guerrier, a half-blood Cheyenne
Thomas Adkins, courier
Moses "California Joe" Milner
Custer in his "Life on the Plains" wrote that he first met Joe near Fort Dodge in October 1868 just prior to the Washita attack:
"He was a man about forty years of age, perhaps older, over six feet in height, and possessing a well-proportioned frame. His head was covered with a luxuriant crop of long, almost black hair, strongly inclined to curl, and so long as to fall carelessly over his shoulders. His face, at least as much of it as was not concealed by the long, waving brown beard and moustache was full of intelligence and pleasant to look upon. His eyes were undoubtedly handsome, black and lustrous, with an expression of kindness and mildness combined. On his head was generally to be seen, whether awake or asleep, a huge sombrero, or black slouch hat. A soldier's overcoat, with its large circular cape, a pair of trousers, with the legs tucked in the top of his long boots, usually constituted the make-up of the man I selected as Chief of Scouts. HE was known by the euphonious title of "California Joe"; no other name seemed ever to have been given him, and no other name appeared to be necessary."