If you set the value of the metabox to the authors cpt post id, you should be able to get the post with
//get the id for the actors cpt
$actors_id = get_post_meta( $post->ID, 'nt_getactors', true );
//get the post obejct for the author
$actors_post = get_post( $actors_id, OBJECT ); //or ARRAY_A if you want an array and not an object
//to output e.g. the title use
$actors_post->post_title;
See get_post for further options.
Update
Change
$post_options [ $post->post_title ] = $post->post_title;
to
$post_options [ $post->ID ] = $post->post_title;
Update 2
Use your $actors_post post object just like a normal post object. Check the codex for a nice reference of the available member variables.
e.g.
$actors_post->post_content;
Keep in mind that $actors_post data is “raw” and you might want to apply some filters to it, depending on how you are using it; e.g.
apply_filters( 'the_content', $actors_post->post_content );
Update 3
In order to get meta values from the actor post either do this for a single value
get_post_meta( $actor_post->ID, 'ecpt_bio', true );
or (if you have multiple values you can get them all in one array) like this:
$actor_meta = get_post_meta( $actor_post->ID );
//and then access the array element
echo $actor_meta['ecpt_bio'];
Wrap up
Change your callback function to reference the id of the post instead of the title (see Update#1)
//get the id for the actors cpt
$actors_id = get_post_meta( $post->ID, 'nt_getactors', true );
//get the post obejct for the author
$actors_post = get_post( $actors_id, OBJECT );
//to output e.g. the title use
echo apply_filters( 'the_title', $actors_post->post_title );
//output the content
echo apply_filters( 'the_content', $actors_post->post_content );
//get the meta values from the actor post
$actor_meta = get_post_meta( $actor_post->ID );
//and output it like this
echo $actor_meta[ 'ecpt_bio' ];