To run the Bloodstone modules, your best option is Cry Havoc from Malhavoc Press, as others have mentioned. The combat system is an excellently-scaled up version of standard d20 combat, and thus you won't have a particularly hard time converting the modules.
In general, a combination of Cry Havoc and Empires probably yields the best combat system; Empires being useful largely for its rules on raising, feeding, maintaining, and configuring armies, and CH for the actual in-combat mechanics. However, when you're starting with prepackaged armies, as you are in the Bloodstone modules, the Empires rules aren't really relevant.
drnuncheon: You're right about the square facing rules not scaling up very well to mass combat. However, it's easy enough to create a "close order" rule that allows any unit to halve its facing along any single axis without penalty, which is what I do IMC.
