Publish and save specific postmeta to a filtered post_type

Do the check inside the callback. save_post will pass you both the post ID and the post object:

do_action('save_post', $post_ID, $post);

So…

function save_my_meta_box_to_postmeta($post_ID, $post) {
  if ('yourtype' === $post->post_type) {
    echo '<pre>';
      var_dump($post_ID,$post);
    echo '</pre>';
    die;
  }
}
add_action('save_post','save_my_meta_box_to_postmeta',1,2);

You may want other conditionals as well like !DOING_AJAX, for example.