I've since increased the title length limit to 150 characters, and if possible I'd like to reimport those old thread titles into Xenforo. I did preserve content IDs when importing.
I'm not sure what the easiest way to do this is. I was thinking just grabbing the thread IDs and titles from the vB copy and truncating the remaining titles at the new 150 character limit. Then insert those updated titles into the corresponding IDs in the XenForo database.
Has anyone done something like this? I'm not sure of any pitfalls I might be facing with that approach.