The turtle mentioned in the Dark Tower series is, of course, the Turtle from It, that helps Bill and the others when they are facing It's real self

From The Waste Lands:

Eddie and Susannah are on their way to the Cradle when the Pubes attack them (so to speak). Once they had killed a few the Pubes stopped but one guy urged them on. He's described as "...bald except for two fluffs of frizzy hair, one on each side. To Susannah, this fellow looked like Clarabell the Clown; to Eddie he looked like Ronald McDonald..." In "It" (also from signet, on page 12) George sees Pennywise in the drain and thinks that he looks "...like a cross between Bozo and Clarabell..." and says that had he been alive a year later, "...he would have surely thought of Ronald McDonald before Bozo or Clarabell." And Pennywise is described as having "...funny tufts of red hair on either side of his bald head..." I belive that the man in the mob who Eddie shoots is Pennywise, or a version of him.

The Crimson King's true form is said to be a spider, like Mordred Deschain. In Stephen King's IT, Pennywise's truest form we see is a spider, his greatest enemy is the Turtle, as in Maturin the Turtle, and can shapeshift, suggesting that the Crimson King and IT are of the same race.

Henry gets picked up by a 1958 Plymouth Fury ( obviously Christine ), driven by the dead Butch Huggins. This alludes to Christine being controlled by Pennywise, who has some sort of connection to the Tower, and Roland's universe. It may explain what actually did control Christine.