The mug shot of Louie "The Lip" Maneri is a picture of Nathan Fillion in disguise.
When Castle and Beckett go to question Harold for the first time, Harold mistakes Castle for the captain of the precinct. To keep up the ruse, he has a desk nameplate reading "Captain Castle" made. The nameplate reappears on Castle's office desk at the loft in the future.
To get Harold to cooperate, Castle suggests redecorating the precinct to make it appear as it did in the 1970s. While it's likely a coincidence, the '70s sitcom Barney Miller (1975) was set at the NYPD's 12th precinct; an even more amusing coincidence is that the series featured Ron Glass, one of Nathan Fillion's co-stars from Firefly (2002).
The title references That '70s Show (1998). Laura Prepon, who played Donna Pinciotti in that series, appears in Nikki Heat (2011) as Natalie Rhodes, the actress cast as Nikki Heat in the film adaptation of Castle's book "Heat Wave".