Control their destiny
Montana - @Weber, vs EWU, @PSU, vs MSU. I think the Grizzlies control their destiny, undefeated and Big Sky conference champions capping the year with a top 5 win (presumably) against MSU would vault them over Tarleton on accounts of winning a far stronger conference and by then they should be ahead of Tarleton in Massey, SoS, and Sagarin too.
Tarleton State - @ACU (ranked 24th), bye, vs N. Alabama, vs Austin Peay (ranked 22nd). Tarleton is probably winning out, if Montana stumbles they've probably got the 2 seed locked down even though some other 1 loss teams could have far better SoS / Massey / Sagarin arguments. I just don't see the playoff committee seeding a 1 or 2 loss team over an undefeated Tarleton.