More comments on the military:
=BRAZIL
Kinda weak military. Lots of regular infantry and nice airforce (probably the best in the region), but few thanks and specialized units. Navy is also poor, some 7 destroyers, 2 battleships, 4 subs and 2 aircraft carriers. Military is very concentrated in the south, so the Pampas should have a bad time with Brazil, while the Front has the upper hand on the Amazon...
=ARGENTINA
Few infantry too, lots of Intelligence officers. Good naval force compared to Brazil, give them some 12 destroyers and 6 subs. Also a good set of Marines, perhaps a transport full of them. They also lead the region with their Condor missile program. Most of their military is in the Buenos Aires region.
=VENEZUELA
Lots of infantry! Venezuela's military expanded greatly with Chaves, so don't be shy with infantry, some tanks and several helicopters. Airforce is the weak point there. If you're feeling evil, you can give them a secret nuke...
=BOLIVIA
Much like Venezuela, but weaker. No Navy and very poor airforce, but good infantry. Focus these units in the "North Chilean" invaded region, so that the capital is rather vulnerable to a Brazilian/Argentine attack. Bolivia has lots of oil, just like Venezuela.
=AMAZONIAN FRONT
Lots and lots of infantry, maybe some jeeps and light tanks. If you're following my suggestion by making the Amazon river navigable at least until Manaus, give them a destroyer sieging the city.
=PLAN COLOMBIA
The greatest armoured force in the region, though poor in infantry. Some helis and jet fighters too, and good Navy.
=PAMPAS
Lots and lots of Gaucho cavalry. Southern people have a great sense of territory and will take arms to defend their homes; while most of them have a strong connection with the cattle raising plains. Some tanks and tucanos (there was a huge brazilian base on Canoas, which was captured) but no navy at all.