'73 (and up?) radiator overflow bottle?

This is the only pic. I have(it,s old one)PO painted the bottle black,I don,t know why.This is in a 73 Dart Sport 340 car,there is a metal strap with 2 little bolts on it that attach to the rad support.Not a very specific pic. but hope it helps ya with location?

My Car 003.jpg