Cast the Adults for Part 2

The only correct answer for Beverly is Amy Adams.

Bill: Elijah Wood, Tobey Maguire or Ryan Gosling
Bev: Kristen Wiig, Amy Adams, Molly Ringwald, Adrienne King or Suzanne Vega
Mike: John Boyega or Donald Glover
Eddie: Lee Pace or Ethan Hawke
Stan: Tom Hiddleston or Ryan Gosling
Richie: Paul Dano
Ben (still fat): Jonah Hill, Kevin James or Billy Gardell
Ben (thin): Jerry O'Connell (yeah, I know)

I guess that'll do.

They shud all be played by Eddie Murphy

I think Chris Pratt simply has to play Ben. Though you can't then have Bryce Dallas Howard as Bev because...well duh. :p I have to say Jessica Chastain is the no.1 choice. Even the young actress who plays Bev wants that to happen, so I'd say it makes perfect sense. So my list would be -

Bill: Joseph Gordon Levitt
Ben: Chris Pratt
Bev: Jessica Chastain
Mike: Jason Mitchell
Eddie: Aaron Paul or Toby Maguire(?)
Richie: Matt Smith
Stan: Shia LaBeouf (you know this to be true...:p)

Also!

Henry Bowers: David Harbour
Audra Denborough: Karen Gillan (why not? :D )

Here are my picks, based entirely on which currently late 30-to-early-40s actors the kids in this film (kinda) look like.

Bill: DJ Qualls
Bev: Maggie Gyllenhaal
Mike: J. August Richards
Eddie: James Ransone
Stan: Johnny Galecki
Richie: Matt Bomer
Ben: Tyler Labine

Bill = John Cusack
Richie = Sam Rockwell
Stan = Nick Stahl
Eddie = Tobey Maguire
Henry = Rob Lowe
Bev = Katharine Isabelle

I think some of the suggestions are too ambitious budget wise. I can imagine a 100m budget at the max but probably nearer 80m (the first part cost around 35m). So names like Chris Pratt, Amy Adams or Ryan Gosling whilst interesting choices would probably be out of range. So with this in mind

Bill: David Harbor
Bev: Jessica Chastain
Mike: Don Cheadle (on the old side - but in the book Mike had aged the most from staying in Derry)
Eddie: David Tenant
Stan: Topher Grace
Richie: Rhys Ifans
Ben: Dominic Cooper

Bill: Ryan Gosling
Bev: BDH
Mike: Ray Fisher < good shoutout)
Eddie: Charlie Cox
Stan: Ben McKenzie
Richie: Martin Starr
Ben: Sean Faris (lost weigh because bev rejected him and got hot)