Radiator overflow tank

hey guys I got a 1970 dodge dart with a 318 in it...I don't have a radiator overflow tank any recommendations that work for you guys?

I made a recovery tank out a shotgun shell thermos.
Plumbed it in the bottom and drilled inside the opening between the layers for the vent, which also exits out the bottom between the tank layers.
Works perfect.

D3D9140D-E026-41AD-8DF2-667AA21E8138.png