> I just want the simplest way to make my window full length -
> something I could put in my .emacs or code into a function 
> that can be bound to a keyboard operation.

Not sure what you're asking.  And I think maybe
you mean Emacs "frame" when you say "window".

Anyway, maybe something like this is what you're
looking for:

  maximize-frame-vertically is an interactive compiled
   Lisp function in ‘frame-cmds.el’.

  (maximize-frame-vertically &optional FRAME)

  Maximize selected frame vertically.

https://www.emacswiki.org/emacs/download/frame-cmds.el