The 383 looks like it is '67-'69 era, mainly because of the turquoise paint. The small block cars were turquoise from '70-'74ish. The paint is original? Read us off that fendertag code when you get the car home. I hope you are keeping that bizarro tan interior, even on a Go Mango machine that is still fairly rare.
Great find man, I hope my challenger will show up soon!