It would be even better if he could engage some of the 35% of the population who failed to vote at all.
A lot of these people hold the view that there's no difference between politicians and to be honest i think they've been right. The Labour party have just been Tory light since 1997
Thing is, if the voter turnout got back to 75% then for Corbyn to win he'd have to keep every current Labour vote and then win half of all of the new people, then win an additional number of voters to match the split in the other half he didn't win that would vote Tory.
The only way Labour can win an election is to take votes from either the SNP or Tories. Not sure which one Corbyn would dip into but you'd imagine it would be more SNP than Tory