Everything old is new again. The Sacred Baby Mountain "legend" was discussed in 2011 and Forum member JDL noted that "It seems to me that further investigation would require discussion with Dr. Tuklo Nashoba, the author of the account, to determine his sources, and some digging into territorial and tribal records from the period. Dr. Nashoba titled the story as a Legend, and authorized its use by the TBRI, stating that the "ITS-BIG" site containing the Legend "was mostly for fun". Dr. Nashoba's site no longer appears to exist." (Emphasis mine.) JDL's comment is on page 5 of a thread on violent Bigfoot, here...
According to a 1949 history in a local newspaper, the Choctaw Lighthorsemen weren't organized until the 1880s and while I'm no horseman, it doesn't look like those are draft horses (or 7-foot tall Indians).
UPDATE: Well, the photo caption states that the Chocktaw lighthorsemen were organized in 1824. So that does fit with the narrative. Still looks like average adult humans on skinny horses, though.
From the Enid (OK) Morning News on December 11, 1949.
From the Atoka County Times (Atoka, OK) on July 02, 2003.