BJ has been out too long now. He's coming off 2 losses, hasn't won a fight in 4 years and hasn't fought in 2 years. Even a fully healthy, in shape, motivated, ready to go Penn that doesn't have a few years of ring rust would have a 50/50 chance at winning this fight because Frankie has showed he can in fact beat Penn... twice (although some controversy).
Honestly, I see no way BJ wins this fight. I hope I am wrong, I'd blow a freaking gasket if he won, jump for joy... but no, I do not believe he will win this at all.