The other prominent conspirator was Artur da Costa e Silva, also a division-general and former commander of the IVth Army, who now only had an irrelevant bureaucratic post. He wasn't as influential but proved himself ambitious in the post-coup power struggle, winning himself the Presidency a few years later. He represented the "traditionalists", who were tied to less dynamic elites, such as landowners, had no complex socioeconomic project and saw the coup only as a reaction against communism, land reform and so on. Mourão Filho, Kruel and Justino, commander of the IVth Army, were all "traditionalists".
There was a third faction, the right-wing extremists, but those are of little note.

Yet despite this the coup d'état could not begin from Rio de Janeiro. Not only did the government's "apparatus" reserve higher posts for loyal commanders, but those were concentrated in Rio de Janeiro (with the unfortunate side-effect that in other places commanders were sometimes untrustworthy). The regime's grip was too strong. So they could only coordinate with another state to come from the outside.

There might be a bit of administrative confusion here. Prior to 1975 Rio de Janeiro state encompassed everything but Rio de Janeiro itself, which formed Guanabara state. Rio de Janeiro state was ruled from Niterói, on the other side of the bay.
The Ist Army's order of battle for Rio de Janeiro and Guanabara was:
FIRST ARMY, Rio de Janeiro
-Âncora, a reliable legalist but in fact had no will to quell the uprising
1st Automatic AA Gun Group, Rio de Janeiro
1st Caçadores Battalion, Petrópolis
-Kerensky, a legalist to the end, almost fought Mourão Filho's troops. However his officers were rebel sympathizers which would prove very important.
4th AA Gun Group, Niterói
ARMORED DIVISION, Rio de Janeiro
1st Tank Battalion, Rio de Janeiro
2nd Tank Battalion, Rio de Janeiro
3rd Tank Battalion, Rio de Janeiro