Green Beast is working to make v3 of their Secure Accessible Contact Form available as a plugin. In the interim, I have discovered how to make it work from a page template.
First, create a page template using include('gbcf/form.php');, then create a page in WP and assign the template to the page.
Next is upload the 'gbcf' folder to the root of the theme directory. Then set GBCF in both form.php and functions.php to call the template directory plus the gbcf directory:
$set_directory = 'wp-content/themes/the-theme/gbcf'
Once that's done, change the "name" field to something unique (like gbcf-name) in both form.php input field, and functions.php where it gathers the POST data.
WP uses "name," and cannot be used by the GBCF script.
Hope this helps someone.