The Porsche 911 Red Book 3rd addition states: "the first thee digitswere the mod.#
the forth digit was the year, the fifth digit identified engines as follows: 1= 911, 2=911S US, 3=911S 4= Carrera US, 6= Carrera, 7= Turbo. The sixth digit was body style: 0=Coupe, 1= Targa. The remaining four digits wew the individual build numbers in sequential order."
You need to get the Red Book.
www.motorbooks.com