[kh99]

Maybe try this:

PHP Code:

ob_start();
   include('custom/header.php');
   $custom_header = ob_get_contents();
ob_end_clean();
vB_Template::preRegister('template_name', array('custom_header' => $custom_header)); 


(of course change 'template_name' to whatever template your want to put your custom header in.

And then in the template:

{vb:raw custom_header}

Here's an article about that: https://vborg.vbsupport.ru/showthread.php?t=228078


I don't know why the other things you posted didn't work - I learned a couple things about php just trying to figure out your code.