mojoPortal always seems to use 443 when it sees https in the url
mojoPortal has no control over what ports it runs on, it cannot choose ports, that is controlled by IIS.
I have not tried using an alternate port for SSL in a long time though I know for sure it worked at one point.
What I do know is that using non-standard ports on a public facing web site is a bad idea. Many corporate firewalls will only allow standard ports for their users so it will not be possible for those users to access your site on a non-standard port
Hope it helps,