I am too scared to try and update the original forums to the newer version of phpBB (3.2). It is required as the recently installed php 7.2 on the server doesn't work with the very old phpBB 3.0 version that the old forum is using. The new version of phpBB is 3.2 on this forum. I have completely backed-up the old forums and verified the back-up so we are okay there. I will leave them alone so that we can still use them as reference.
Any thoughts or concerns with this approach? There is still time to come up with alternatives going forward.