I cann look around, lotsa people probably got spare e50 cases so post up for one in buy sell. it's a good idea to run a matching pair but you could probably get away with just replacing the bottom half. Then rebuild cuz it's easy and good learning and good practice, and you can case match while you're in there to move up to a better kit.
That extra hole i've seen, can't remember if it was an e50 but it's basically a case drain if like the carb or oil leaked all into the cases for some reason. not a biggy, i wouldnt touch it.