I'm not sure when they changed this, but in 1947 the door handle locks the door when the handle is turned towards the back and unlocks the door when it is pushed forward. I also looked at the battery cover and space is very limited in that area although it could be an option. The latches are original as far as I know. I will check things out and try the window method as EchoBravoSierra suggests.

It's a small world, but I wouldn't want to paint it.