I just went through this on my 68 Mustang.
I would do as texasking suggests above, if possible. The gas door is a great option on that car since it’s covered by trim and wouldn’t be faded.
I didn’t have a sample to use. I ended up using Nason Ful-Base. My paint store changed the “binders” to convert it from a single stage to base. Nason isn’t the best per the folks on here, an I am a novice but three coats it’s covered and looks good under SPI universal clear.