Redirect Restricted Page to 404

I was able to display a 404 error by using the following code in my header.

<?php
  global $wp_query;
  $wp_query->set_404();
  status_header( 404 );
  get_template_part( 404 ); exit();
?>

To break it down:
$wp_query->set_404(): tells the wp_query this is a 404, this changes the title
status_header(): sends a HTTP 404 header
get_template_part(): displays the 404 template