Which version of Cerdan? He was a welter for a while early but blossomed into a middle later. How many rounds? I'm sure Judah would last some rounds against that later version but would likely be worn down to either a decision win or stoppage. I don't think much of Cerdan compared to most but this isn't exactly a tall task for a full blown middle who beat guys like Holman Williams, Georgie Abrams and Tony Zale.
Cerdan would be losing to Judah until suddenly he wouldn't be. Eventually his superior physicality , strength great chin, consistent pressure, better than average skills would lead to a ko win over Judah with in ten rds.
Zabbidy Doodah He does the slappy dance of combos on Cerdan early and then hoofs it , sadly the only chance for Cerdan is for a KO in the later rounds. I think Zippy wins a controversial decision as he staggers to the final bell. Cheers