The Wagon-Box Fight is one that really interests me, but it's a very a tricky one to game, because essentially it's a small number of defenders in a very small and static defensive compound beating off multiple waves of huge numbers of warriors. Given that only 32 white men were in the wagons and many hundreds of warriors were attacking, both on horseback and on foot, it's hard to see how one would scale it in order to give the attackers enough models.
It's also tricky to game because of the alleged impact of the new Springfield breech loading rifles on the fight, as the firepower/rate of fire was apparently unexpected for the Indians, and prevented enough warriors from closing and thereby prevented their numbers taking effect. How to simulate that within the chosen rules would be interesting in itself. Not only that, but how to make it interesting enough for both sides so that there is some tactical challenge (other than 'defender just sits and shoots/attacker just tries to close in'.)
The Plains Indian Wars of the 1850s and 1860s are, to me, much more interesting than the later conflicts, but they are very hard to game due to disparity of numbers and the Indian tactics/attitudes to the fighting - the fact that they often vastly outnumbered the soldiers, but relatively rarely made those numbers count, despite their vast superiority in fighting ability compared to the average American army recruit just isn't catered for in many rules as far as I can see (probably because it's so difficult to simulate).