Don't think they came with one, but what is being used as an overflow tank?

 

You can buy a generic tank if you like. They range from cheap plastic ones to expensive exotic metal. If you do not over fill the radiator there is no need. There is a cold fill line on the right rear side of the radiator.

 

Something like this.

 

There's a picture in this other thread showing the bottle I used in my 67. You will need to change to the correct radiator cap also if you use an overflow.
https://classicoldsmobile.com/forums...flow-tank.html