Post with Custom Permalinks

You could use the Rewrite API. Since you have a fixed set of posts you could do the following:

 add_action( 'init', 'rewrite_old_slugs' );
 function rewrite_old_slugs(){
    $post_slugs = array(
        'post-1' => 1,
        'post-2' => 2 
    );

    foreach( $post_slugs as $slug => $new_id )
        add_rewrite_rule( $slug . '?$', 'index.php?p=' . $new_id, 'top' );
 }

I’ve created a post_slugs array where the array keys are the old slugs and the array values are the post ids.

If you go this way, you have to go to Settings > Permalinks and hit the update-button, so the rules are active.

This solution works for posts. If you need it for pages, you need to rewrite the URLs to

index.php?page_id=