With MAMP Pro, you are able to register virtual hosts to any location. That is partly why you want to switch to default ports because your browser already assumes 80 as the http port... this will allow you to just enter the name of the virtual host without any additional port information and be directed to the site on your testing server.
On MAMP Pro, for example, the disk location for localhost will be /Applications/MAMP/htdocs as you stated earlier... but now, you can add hosts by using the plus button and setting the disk location to whatever you want... for example, my SOJO web site is mapped like this: /Users/(user_name)/Sites/sojoweb.com/public_html
As you notice, I set my testing server version of my site to be exactly the same as my production server. The only difference is what I named the virtual host - sojoweb as opposed to sojoweb.com