Would asymmetric cryptography be feasible in World War II?
Sure, you can do Diffie-Hellman or RSA by hand if you have to.
And you don't need the bit length we use today with powerful adversaries.
I'm not an expert on WW2 computational machines but I won't be surprised if something to do modular exponentiation could be built using WW2 technology given sufficient motivation.
A modern cryptographer in WW2 could make truly unbreakable ciphers. With authentication, key exchange, good randomness, and all the good stuff we have now.