Hello,
I got excactly the same problem.
Have bought iMac27 (2017 Modell) with VESA mount withiut knowing that it comes wirhout stand. Seller refuses to take it back.
@Garret: did you succesfully mounted the original apple stand by yourself? Where did you get the original stand and the mechanics (and maybe the screws)?
Is the imac tiltable with your setup?
Andre@fluxguide.com