I need to set a custom template for a custom post type with standard wordpress functionality like this: Creating_Your_Own_Page_Templates
I found these: 1 – custom post template , 2 – single post template , but its not working for a custom post type and this works only for built-in wordpress posts.
I went through the same problem a few months back. After several different ways I finally found a way that worked. Try adding this to your themes functions.php file (be sure to replace both instances of portfolio to match the actual names you use):