I had a quick look at this and it appears that you are going to run into a few path problems.
Just a small example:
$template->set_filenames(array(
"body" => "admin/wordpress_admin_body.tpl")
<img src="../templates/subSilver/images/wp-united-logo.gif"
These and other paths don't exist and neither is the folder structure the same as phpBB. You should be able to clone a style as subSilver and use the config as KasLimon suggested, but you would also have to add an Admin folder to that style, rename the .cfg to subSilver.cfg and install as directed.
Noting that login.php is now login_ip.php etc.
At best it's a messy way of doing things, and maybe someone who is experienced with WordPress would like to re-write some of the script to integrate it properly into IP. ?
Not Me!
Edit: Your title to the question may also be better if you changed it to "Need Help Integrating Wordpress" then the more advanced coders may take a look at it.