I'm probably a little biased, but I believe Buicks as a whole are grossly undervalued. The GSX cars should be compared favorably with LS6 and Hemi cars. There are a few resources that will help determine the authenticity of the car. Take a look at
www.v8buick.com
In 1970 ther were only two colors available on the GSX: Saturn Yellow and Apollo White. Take a look at the trim tag. Good luck.