Freaks was an American horror film released in 1932. The film tells the story of two 'normal' circus performers who plan to murder another performer in order to gain their inheritance. Much of the cast was comprised of real life carnival performers with deformities. The twist to the film is that the 'freaks' are decent and trusting, whereas the 'normal' characters are the real villains.
Louis Antoine de Saint-Just (1767-1794) was a French revolutionary and military leader. He served on the Committee of Public Safety with Maximilien Robespierre, and was deeply involved in the Reign of Terror. He was executed along with Robespierre in 1794, at the age of 26.
Grossout is 1960s slang for being disgusted by something or making someone else feel disgusted.
This is not just a generic reference to the Porky Pig character; Pynchon is referring to a specific cartoon, 'The Blow-Out' (1936). It was directed by Tex Avery and animated by Sid Sutherland and Chuck Jones. At this point, Porky Pig was still voiced by Joe Dougherty, before Mel Blanc took over the role in the late 1930s.
In 'The Blow Out', a young Porky Pig is doing favours for people to raise money for ice-cream. He crosses paths with the Mad Bomber character and, thinking he has dropped his bomb by accident, keeps returning it to him until the inevitable explosion.
Pynchon also referenced this particular cartoon in The Crying of Lot 49. The image of Porky Pig returning the bomb is mentioned later in Gravity's Rainbow as part of a hallucinatory montage.