I am just nearing the end of the book "The Earth is Weeping" by Peter Cozzens.
Story of the Wars in America against the plains Indians. A very harrowing read at times. The cruelty of some Indian warbands and US treatment of Indian peoples by deception and lies is shocking in equal measure.
However the accounts of some of the battles, most little more than skirmishes, has fired my imagination. I am now wondering what the best DBA rules set would be to play these battles.
At the moment my thoughts are, adapt DBA 3.0 myself, use HotT, or Horse,foot and Guns.
"I would rather have a russet coated Captain who knows what he fights for and loves what he knows. Than he who calls himself a gentleman, and is but little else." Oliver Cromwell
I would think a skirmish set would be more useful. I have to admit to almost no knowledge of the period but presume raids on villages, settlers and supply columns were more numerous that full on battles or so Hollywood always told me. Baccus have released some 6mm pony wars and possibly a rules set. 6mm may be too massive for you though.
If going DBX i would use HoTT and exclude things you dont want like flyers etc.