Assuming you kept ids intact as part of XF install options, it's pretty easy if you still have the old (vb) database still intact and you have the XF redirector scripts (with the vb names) in place...
I used this to get my forums in my vbseo format and basically just build a 'rule string' to copy into excel as text and finagle a little bit into a rule set for htaccess (you may have other conditionals for special characters to include or used different replacements, so alter as necessary.) If you used nested like /forum/subforum/ cat urls, this won't work for those
"Redirect 301 "
, replace(replace(replace(replace(replace(replace(lower(title_clean),"'",""),":",""),"/","")," ","-"),"--","-"),"->","")
Then just kinda take that data dump into a text file and fine tune it a bit.