Castiel uses the name James Novak (the name of his vessel) to rent the house where he and Kelly are hiding out.
The Title of this episode "All Along the Watchtower", is a reference to the 1967 song (of the same title) by Bob Dylan. Although this is Dylan's song it's strongly identified with the interpretation The Jimi Hendrix Experience recorded.
This episode references episode 6.15 "The French Mistake."
This episode was the final work by stunt coordinator Lou Bollo before being succeeded by Rob Hayter for the series' final three seasons. It is also the last work in Lou Bollo's lifetime before his passing in 2022.
When Dean says, "Say hello to my little friend", that's a quote taken from the movie Scarface (1983) just before the main character, Tony Montana (Al Pacino), blows the doors off of his office with a grenade launcher, killing would be assassins.