Oh, it didn't occur to me to look into a board titled "archives". Wouldn't that indicate the contents are not current? I was only looking in the 3.1 and 3.2 boards.
(I think we might be calling "boards" and "forums" oppositely. I think of a forum as being made up of several boards.)
Following your link, and finding an SMF converter, I find the last message in that thread was Dec 2016, and the last successful conversion reported there was for SMF 2.0.11. But the current version of SMF is 2.0.15. And I did find messages in the 3.1 and 3.2 boards which indicate someone trying to update the 3.0 converter, with no success (well, it sounded like part success, but not a workable, usable result).
The latter indicates:
A convertor to phpBB 3.2.2 doesn't exist yet. You have to convert to a lower version and then upgrade phpBB.
The problem I will have is that I won't have a choice to install 3.0. I'm investigating adding contents of my SMF forum, to an existing phpBB 3.2 installation. I think we'd have to install 3.0 on the server, beside the existing 3.2 forum. Then upgrade the 3.0 to 3.2. And then merge from the new 3.2 forum to the pre-existing 3.2 forum.
Generally speaking, does that seem like the best and most workable solution? (I don't think we will have time and/or the person-power to do that, but just in case, I want to make sure that would be a workable plan.)