Ring linking with custom post types?

Question

Search Engine Optimization

I have a code which I use for ring linking.

<?php
/**
 * Plugin Name: Линковка проектов
 */
function circular_links_post_ids($n){ // Линковка проектов 
  global $post;
  $nDisplay = $n;
  $cats = wp_get_post_categories($post->ID);
  if ($cats) {
    $args=array(
      'category__in' => $cats,
      'posts_per_page'=>-1,
      'caller_get_posts'=>1,
      'orderby'=>'date',
      'order'=>'ASC',
    );
 		$myposts = get_posts($args);
    foreach($myposts as $position=>$mypost){
      if($mypost->ID == $post->ID){
        $currPosition = $position-2;
        break;
      }
    }
    $total = count($myposts);
    $postsCount = $total - $currPosition;
    $postIDs = array();
    if($postsCount >= $nDisplay){
      for($i=0;$i<$nDisplay;$i++){
        $postIDs[] = $myposts[$currPosition+$i]->ID;
      }
    }else{
      for($j=0;$j<$postsCount;$j++){
        $postIDs[] = $myposts[$currPosition+$j]->ID;
      }
      $firstPostsNum = $nDisplay - $postsCount;
      for($z=0;$z<$firstPostsNum;$z++){
        $postIDs[] = $myposts[$z]->ID;
      }
    }
    $array2 = array ("ID" => "$post->ID");
    $postIDs = array_diff($postIDs, $array2);
    return $postIDs;
  }else{
    return false;
  }
}

function circular_links($numb){ // Линковка проектов 
    $orig_post = $post;
    $postIDs = circular_links_post_ids($numb);
    $args = array(
      'post__in' => $postIDs,
      'order' => 'ASC'
    );
    $my_query = new WP_Query($args);
    while( $my_query->have_posts() ) {
      $my_query->the_post();
      ?>
      <?php 	get_template_part('parts/card-project2'); // шаблон карточки проекта ?>
    <?php }
    $post = $orig_post;
    wp_reset_query();
}

How can I convert it to custom post types and custom categories?