Custom html.tpl.php file is not getting picked up
You have to add a theme hook suggestion (example from here):

function THEME_preprocess_page(&amp;$variables) {
  if (isset($variables['node']-&gt;type)) {
   // If the content type's machine name is "my_machine_name" the file
   // name will be "page--my-machine-name.tpl.php".
   $variables['theme_hook_suggestions'][] = 'page__' . $variables['node']-&gt;type;
   }
} 


Use this in code in your template.php file in the theme directory and, obviously, change it :)