Hi Jay,
The only place I've seen this documented is in the article written by LeRoy Hafen in 1952, I think, which you've probably already seen. It's located here: http://stvrainsfort.homestead.com/LeRoyHafen.html
Other than that I personally have confirmed that there is an Arapahoe Chief Friday buried in Fort Washakie, Wyoming that would be about the right age. Hard to say. Marcellin did, it seems to me, leave suddenly about then and never came back. It's a facinating mystery.
Joe Pinner
Greeley, CO