Nevermind, ended up writing it myself. Here it is for anyone else in need of it.
RewriteRule ^members/([^/]+)\.([0-9]+)(/)?(.*)$ https://fearlessrevolution.com/memberli ... ofile&u=$2
RewriteRule ^threads/([^/]+)\.([0-9]+)(/)?(.*)$ https://fearlessrevolution.com/viewtopic.php?t=$2
It will redirect threads/blah.831/ and even threads/blah.831/#post-3255 without fail but append the #post-3255 at the end. I couldn't figure out how to remove that and wasn't bothered anyway since Google mostly cares about the topic id. Will also redirect pages without fail but not to the correct page so you do end up with the correct 301 to topic but NOT to the correct page.
Now hoping Google notices it and reindexes the member profiles. They were indexed but with nothing showing up.