I have a couple rings of 50's amd 60's GM keys I use to check locks on junkyard cars. Every once in a while they find the right hole. Give me a call and I can send them for you to try. If you find one that fits, it should work for all locks in 1964, make a copy and you are set. The other option is take a door lock out and have a locksmith get the numbers on the cylinder and make one.
overspray