There's more to it than that I'm afraid. (first of all, any PHP code needs to be inside of
<?php ?> blocks.)
$object determine the metabox context, these need to be defined. All the
do_action() call does is ask the theme and plugins to add their meta box callbacks (for the particular context) to the global
$wp_meta_boxes. Your code would need to step through this global, extract the required information, and use it to build your dropdown and setup whatever else happens when the form is submitted.
I'm not sure exactly how the global is structured, you'll have to var_dump it and study it for yourself. Welcome to WordPress development :)