The old one might be worn enough to work with another key. If you can find one that will work turn the switch then insert a paperclip into the hole. You should then be able to turn it a little more and get the switch out. Which way to turn it depends on the particular switch but I believe he '49 just had on and off.
Another option would be remove the door lock. It probably has a key code stamped on the outside. Have a key made to that code.