Is it a rectangular plastic tank that rested in a wire bracket that was attached to the passenger fender,? Does it have value?
Gary, the overflow was not a factory option in 68, the 69 model had the overflow fender mounted unit and dealers would add it to the 68 models for clients, but it was over the counter for the 68 models The small one you are referring to was also an over the counter item that could be used on the cars, it was not overly popular
There was a service bulletin authorizing the fitting of the 1970 radiator overflow tank on '68 and '69 cars.
Randy Brooks installed one on the 68 GS400 convertible I purchased from him. He had a service bulletin- I think its in all the docs he gave me.