Che Guevara won't succeed in Bolivia, as he lacked any type of local support.
The issue is keeping the Latin American armies loyal to their own governments instead of the American one. But even if that's achieved, they would still fight communist guerrillas and succeed, as they simple have a lot more resources at their disposal. Should that fail, or a democratic communist party ends up winning elections and the military remains loyal to such government, then the USA can invade the country, as they did with Granada and tried with Cuba.
I'd say only the larger South American countries have a chance of remaining red - Chile is the best case if the Armed Forces remain loyal to the government. Regarding Mexico, whatever the POD, the USA won't let a Soviet ally exist on its southern border.