radiator overflow or make up tank on 1936 Ford Coupe

[JayMan!]

Recently I purchased a 36 Ford coupe and discovered there is an overflow tank mounted on the firewall. One of the plastic tubes from the bottom of the tank is connected to a port at the bottom of the radiator. The second tube from the top of the tank goes to the ground. I know the 36 Fords did not have overflow tanks so I was wondering if this tank may have been added as a coolant make up reservoir, and is the reason the tube coming out of the bottom of the tank is connected to a port added to the bottom of the radiator. Has anyone ever heard of this? Thoughts?