During a manga chapter where the characters are trying to escape from Baron Ashura's submarine, they start joking about stripping like in Harenchi Gakuen.
Dr. Hell's final Humongous Mecha is named Great King of Hell and it has three faces, right like Satan did in the The Divine Comedy. Go Nagailoved that book (albeit he apparently did miss that there are two parts after Inferno), and not only he included references in many of his series but also he drew a manga adaptation.
Archduke Gorgon's Youkikaijuu often look like Greek gods (Apolon A1) or mythological creatures: minotaurs (Minos M7), unicorns, (Yunikon Σ2), centaurs (Kentol Y7), harpies (Harpy π7), dragons (Draco Ω1)...
Cicero N9, Mechanical Beast of episode 83, is named after Cicero.
The Fem Bots are named after Greek and Roman Goddesses: Aphrodite was the Goddess of Love, Diana is the Goddess of the Hunt, Minerva is the Goddess of the Wisdom, And Venus was the Roman equivalent to Aphrodite.