I'll leave Mourão Filho's part for after I get the books but in the meanwhile I can already give a rundown on Rio de Janeiro and then narrate what happened in São Paulo, the almost-battle in Resende and events in Rio city.

Rio de Janeiro city was by far the highest-value target in the entire country. Most of the federal administrative machinery was still there much of it still is, in contrast all Brasília had was symbolic value and Congress. To win the rebels would have to seize it or at the very least lay siege to it and negotiate. Among this administrative machinery was the Army's supreme headquarters in the Duque de Caxias Palace, housing the Minister of War (Jair Dantas Ribeiro, who was hospitalized at the time rendering legalism acephalous), the commander of the Ist Army and the Chief of Staff.
There were two other key palaces just a short distance from each other: Laranjeiras, a Presidential residence, and Guanabara, the gubernatorial office. On the 31st of March both were occupied, the former by Goulart and the latter by Carlos Lacerda. Lacerda was a famous liberal-conservative whose name is still remembered by anyone with a minimum of historical literacy today, a politically engaged journalist who made the most drama out of his struggles, and took part in the downfall of Vargas in 1954 (when an assassination attempt against him led in a chain of events to the President's suicide) and Jânio Quadros in 1961 and was now in public office. He was set to run as the leading right-wing presidential candidate in 1965. Rhetorically he was Goulart's greatest enemy, a fiery oppositionist. Despite this he was of little importance in the conspiracy to overthrow the President, partly because the governor of Minas Gerais was a competitor within his party for the presidential run and partly out of his own decision as the city's garrison was too strong and he was too obvious of an enemy. But he did know in advance there'd be a coup d'état. At his disposal was the city's gendarmerie.

The city also housed a huge number of conspirators. Most important among them was the Chief of Staff division-general Humberto de Alencar Castelo Branco. Old and very prestigious, he was a veteran of the Italian Front and once commanded the IVth Army. His present position was a great honor and second only to the War Minister, but toothless - he commanded no troops. He was reluctant to join the conspiracy but once he did was accepted as its natural leader. He kept a low profile to take advantage of the "apparatus" not noticing his subversive intent as well as to gain more credibility among his peers when, as someone seen as a legalist, he opposed the government. He set up an informal "staff" for the revolutionary movement and helped tie together the several different plots across the country. As the most prestigious member of the movement he'd succeed Goulart as President.
Among his allies were Ernesto Geisel, President 1974-79, and Golberi do Couto e Silva, mastermind of the surveillance state and personal friend and source of Gaspari. He was a chief example of the "modernizer" wing of the military, who were tied to international capital and the most dynamic elites and had a comprehensive project of social and economic change. He was proud to be part of the "free world" and followed the "National Security Doctrine" which stated the need for the military to preempt a communist revolution with a counterrevolution and then to use capitalist development to fund a strong military (guns over butter) and defeat the internal threat of revolutionary war.