Rewrite rule forward to specific domain and port

You shouldn't need to specify the port unless the application requires it. It's rare but some do. So instead of redirecting on host, you want to silently modify the host header for ingress traffic. You'll definitely need a pool with port 7012 members and modify the host header on every request. The URI change from "/" to "/Portal/index.html" should probably be a redirect though - unless you want to be in the business of managing every possible URI (the work of a rewrite proxy).

when HTTP_REQUEST {
     if { [HTTP::uri] equals "/" } { 
          HTTP::redirect "/Portal/index.html"
     } else {
          HTTP::header replace Host "server.nbc-news.west.foo.com"
     }
}

Again, should you need to completely hide the URI as well, you can use the HTTP::uri command on the ingress, but you have to be mindful of any possible URI translations.