It's on ALL cars.
For 1967 it's shown on UPC 8, Sheet B2, Item 6, for 1968 it's on UPC 8, Sheet B4, Item 6 and for 1969 it's shown on UPC 8, Sheet B5, Item 6. It keeps the fuel line from rubbing against the gas tank strap and basically looks like a 3 or 4 inch piece of foam rubber hose. It was also used on other models and other years as well.
Note that it was also used on the 67-69 convertible parking brake cable to keep it from rubbing against the X brace. (for 1967 and 1968, UPC 5, Sheet C1, item 3 and for 1969, UPC 5, Sheet C1, Item 8.)
Ed