make content by path restricted to anonymous?

situation:
An existing 4.7.* drupal website using a subfolder for drupal. So www.****.com/whatever is a static website
edited with ftp, dav or whatever, and then www.***.com/private/**** is the drupal website with access control
for annoymous removed on everything but frontpage module.

Plan is to be upgrade to 5.* but not 6.* till more modules like TINYmce are available.

Here is the desire. We would like to setup somehow to have drupal(s) do both the 'public' and the 'private' website
designated by a subfolder /private on the domain name.

To have drupal for www.****.com and separate drupal for www.****.com/private I fear may wreak havoc on figuring a sites/***/settings.php configuration.

But it is absolutely essential for anything under /private to not be available for annoymous viewers., hence the thought of having two separate drupal sites.

IF we tried to use some taxonomy module or equivalent to control access but put the 'one' drupal site at the root, /
several issues arise, would need all new content for private, including forums to show up with path /private/****
and several other issues... like uploads will need to be private, system....
ALSO it would be helpful say, anything posted without the path /private/**** meant to be public require user be a privileged role or moderation, because the average user is not carefull about paths..

Suggestions? need clarification of question?