I have all the old forum data but it's in phpbb 1.4.1 and I've been unable to find a viable conversion path.
I believe the proper path is phpbb 1.4.1 to either 1.9 or straight to 2.x, and then 2.x to 3.x however I don't have an old enough version of php to be able to even run 2.x to run the conversion script. I have spent far more time on this than I should have so I'm giving up. If someone comes forth with a working way to convert the old data, that would be great, we can keep that legacy info around in the legacy section of the website until the new engine is good to go. If not, well... it's been 20 years so people probably don't care that much.
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