If you are still stuck, one possible alternative is to get all Post ID’s by the custom post type. You could try something like this:
$the_query = new WP_Query( array(
'post_type' => 'my-custom-post',
'posts_per_page' => -1,
)
));
while ( $the_query->have_posts() ) : $the_query->the_post();
the_ID();
endwhile;
It would require you creating a custom post type, and associating posts to it.
There are ways you can associate page templates to posts, but as far as how WP_Query would work from that point with that process, I still have to learn 🙂