I made some changes..
IN gtcustom_threadrow replace
$thread[lastpost]
with
$thread[lastpostdate]
in the print_gtcustom_newthreads() replace
$thread['lastpost'] = vbdate($vbulletin->options['dateformat'], $thread['lastpost'], 1);
with
$thread['lastpostdate'] = vbdate($vbulletin->options['dateformat'], $thread['lastpost'], 1);
regarding the iframe ...
add a target attribute to your link ie.