Okay, I think that this will do what you want. Put the code below into a Custom PHP block, probably in the bottom side. It will display the page index.
global $scripturl, $modSettings, $context;
$pages = array(
'page1',
'page2',
'page3',
'page4',
);
echo 'Page [ <a href="', $modSettings['sp_portal_mode'] == 3 && empty($context['disable_sp']) ? $modSettings['sp_standalone_url'] : $scripturl, '">', empty($_GET['page']) || !in_array($_GET['page'], $pages) ? '<b>1</b>' : '1', '</a> ';
$i = 2;
foreach ($pages as $page)
echo '<a href="', $scripturl, '?page=', $page, '">', !empty($_GET['page']) && $_GET['page'] == $page ? '<b>' . $i++ . '</b>' : $i++, '</a> ';
echo ']';
You might want to disable the title, body and set the body's style so that the text is aligned to the center.
The index in that block serves as an index of SimplePortal Custom Pages, so you will have to create new custom pages as required. The $pages array is an array of page ids that will be used to create the index, you will need to change that array as required, depending on the ids that you have given to your Custom Pages.
The '1' page is always the normal portal page, so that could also have your articles displayed there.
To get the best effect, you will have to make sure that all your blocks that display on the portal, also display on each page that will be a part of the index.