Just talked to a friend of mine here that has been doing cavalry reenacting for years. He has been used in the Gettysburg serial movie done by Ted Turner and Gods and Generals among others. He has played the Sergeant Major that was the orderly to Chamberlain of the 20th Maine. He is a member of SAG as well (screen actors guild).
He said Ted Turner is doing another movie which starts filming in March in the Shenandoah valley. He is going to reprise his role as orderly to Chamberlain who will again be played by Jeff Daniels. It is going to be about Grant meeting with Sherman after Sherman made his march to the sea. I'm not sure if he knew much more.
Jim said his horse has died so he will end up getting one when he gets there. Only in the movies would you have a 60 something sergeant major <g>. He did say that it was not uncommon for he and others to be unhorsed particularly when the shooting starts.