In 1996 I bought a 1970 Mach ! with a Chestnut Metallic Exterior ( Y- Ford 3347-A ) and Ginger Interior as a restoration project. I completed the restoration and eventually sold the car. It is now in Australia. If I remember correctly Auto Paint Depot in San Diego, CA had the exact match of the original Chesnut Metallic paint. Chestnut Metallic was a Thunderbird color and was offered on Mustangs as a special 1970 Spring
promotion. I have forgotten how many Mach 1 Mustangs were built with the color. But, it is rare. There were only 14 1970 Boss 302s in the color. I believe Auto Paint Depot supplied a PPG mix. I will search for a color code and see if there is still a website.