When DeJesus beat Duran in their first fight, it was technically a junior welterweight fight as they both weighed 138. McGirt's edge in size isn't big enough to overcome the gap in class.
McGirt wasn't fighting in the same day weigh in era and would move up. He was way bigger. I don't buy the gap in class theory. DeJesus lost almost all of his big fights other than the first Duran one. I think his standing gets inflated by those who don't want to admit that Duran could be outboxed. McGirt was actually pfp for a couple years.
McGirt was a very capable boxer. Granted, DeJesus has the better wins on his ledger, but McGirt pushed Sweet Pea Whitaker pretty hard in their first fight, while carrying a shoulder injury. He was one if the top performers of his era and for what it's worth, one of George Foreman's favourite fighters to watch. So personally I don't see a gap in class to DeJesus. I think it's a close fight that could go either way, with a small edge to DeJesus. But McGirt can certainly win this fight.