I think my favourite was the mass combat system in the free d20 Birthright netbook; it looks like a much simpler and easier to use version of the over-complex Fields of Blood system, with a scale of about 100:1.
If you really want to run Bloodstone Pass at 1:1 scale, you should just be able to use d20 rules as-is. I'd suggest using something like the 4e "Minion" rules, where "Hit" = "Kill", the minis on the field represent the unit's "hit points". This probably works best if you use the old Battlesystem approach where each 'round' of the battle is actually 3 rounds of regular combat; ie you run 3 rounds for the PCs, then do 1 round of army vs army.
You could also use the d20 Birthright system's "Hit = Wound, 2nd hit = Kill" approach.
If you really want to run Bloodstone Pass at 1:1 scale, you should just be able to use d20 rules as-is. I'd suggest using something like the 4e "Minion" rules, where "Hit" = "Kill", the minis on the field represent the unit's "hit points". This probably works best if you use the old Battlesystem approach where each 'round' of the battle is actually 3 rounds of regular combat; ie you run 3 rounds for the PCs, then do 1 round of army vs army.
You could also use the d20 Birthright system's "Hit = Wound, 2nd hit = Kill" approach.