Yah. I did delete the testforum database and the testforum folder and then did a freesh testforum install. That created a second forum with none of the categories, topics, members of GVforum and the two forums were able to operate independently. So far so good.
Next I used the internal phpBB restore database function to load in a copy of GVforum's database that was slightly different than the current one because it lacked one forum category (ironically named Humour). That went well and at that point testforum looked like GVforum except for the one category difference I expected, - so my new forum lacked humour . Even better, I was now able to navigate either forum without it getting tangled with the other (as seen in the browser's url bar).
It went bad though when I tried to log in to the administrators panel on testforum and ended up in the panel for GVforum. Also tried logging in as user and found that any attempt to login to testforum takes me to GVforum. Once logged in though I can go back to testforum and everything works OK, I even made a test post. However I cannot figure out how to log on to the administrator's panel in testforum. Always end up back at GVforum.
BTW, the config.php files for the two installs mention different databases and the two forums behave like they keep the databases separate now. Remaining problem is the 'crossover' on login and inability to login to testforum's admin panel.