At 130 or 135. A fascinating chess match between two very skilled southpaws and Olympic gold medal winners. Casamayor was a very tricky technician but would he have been able to handle the more gifted fighter Lomachenko?
Loma's performances against guys like like Russell, Rigo, and Campbell should give a good idea of how well he does against other southpaws but I also think Casamayor would have posed a more difficult challenge than all 3 of them IMO. I still favor Loma to win convincingly by decision but it's a competitive and tough fight throughout where Loma is forced to dig a little deeper.