I totally ran across this thread on accident. But BOY do I NEED it! I have a forum that's probably 20-25 years old and still running strong, and upgraded to SSL (https) last fall...and never did the database on the rest of the site (forum) because I didn't want to crash it. It's so HUGE. so I basically just did the homepage, and some other non-forum pages on the site, but I Really need to do the forum cause it's affecting SEO already having mixed content. Bless you! for writing/starting this thread, and everyone who has contributed to it. I'm a website developer (mostly wordpress) who picked up this client with this old site with this UBBThreads forum on it, and it's been a struggle for me ever since I picked it up, but he really hasn't run across anyone in the area even as knowledgeable as I am, which doesn't say much really.
I'm going to read through this, as I contemplate updating some db tables, gently, one at a time. But if anyone is super-experienced and wants to lend a hand, PLEASE don't hesitate to offer. (LOL)
Anyway, ...GOOD STUFF. :-)