As an FYI.... the link in the User manual for the 645JS does not bring you to the Greartisan motor.... It's a different brand.... Mounts may be the same.
Side note, Printing that base VS the JGY370 I'm finding that I can't use the same screws to secure the (F) Drop hole adapter... What size screws do you recommend for that?
Edit: My Screws are Tiny... like 1.5x7mm