Good idea, that could make a funny campaign. Go on!
Thinking about it, you can edit most of the stuff from the scenario editor, as long as you have US units swapping US weapons (e.g. an M60 with an M1 gun as you said). Try to generate a scenario (any kind) and in the deploy phase hit 'D' with a unit selected, there you can edit the unit's name, weapons, armor, FCS, vision... you name it.
Did you give much thought into the political whereabouts of this campaign or is it just meant to be a wild what-if? (would be fine too, no worries)
I'd be interested in knowing what parts of the country are supposed to break away from what, and why. After all, it's not as if cotton culture was still all the rage these days...
