The screenplay is pretty close to the final movie, with tiny exceptions like Ferris stealing money from his dad and Charlie Sheen's character driving the entire narrative. However, since John Hughes banged the script out in less time than it took to write this article you're reading, there were understandably some kinks to work out -- such as the scene where Ferris visits a f*****g strip club, jumps on stage, and pulls off the most boner-killing Elvis impersonation ever written.
Of course, it may not have felt like a crazy tonal shift, thanks to the magic of editing:
Wait, is this a script or free association poetry?
It's a pretty weird deviation to go from the "live life to its fullest" ethos of visiting the Sears Tower and touring the Art Institute of Chicago to the "live life spending a sunny day inside a dank, neon-filled pit of debauchery" ethos of this scene. Presumably, Ferris thought it was a necessary detour after Cameron nearly burst a blood vessel trying to mentally undress the women in a Seurat painting.
It's basically this, but with "Cherry Pie" playing in the background.