So you want to make individual letter pages for a custom post type.
You can do something like this, find this line around line 230:
$tags = get_posts(array('numberposts' => -1, 'sort_order' => 'asc', 'sort_column' => 'post_title', 'post_status' => 'publish', 'post_type' => $type, 'category' => $from_category, 'tag' => $post_tags));
and you can replace it with: https://pastebin.com/9raX9ncL
and you’re going to want a shortcode something like:
[mctagmap show_posts="yes" css3="yes" post_type="your_post_type_here"]
Notice the css3=”yes”, this is because when css3 is off, the code makes columns based off the number of letters and in this case, you’ll have only one. So you’ll need to style it on your own.
With the pastebin code, you can pass a URL parameter of ?mctag=A and the page will only show the As.