The original system didn’t have an overflow tank, but was available as an option or accessory. They’re out there but pretty pricey.
Here is one from Classic Parts on ebay.
My ‘52 with a ‘59 235 runs with about a 1/4” above the radiator core. Any more it just pukes it out. I fully agree that a coolant tank is a good idea and one that I’m eventually going to install.