You cannot tell from the VIN in 1971 whether a car is a Stage1 or not, in fact, 71 cars are the hardest to document. In 1972, there was a letter code for engine in the VIN, K would be a 350, U would be the standard 455, and V was the Stage1 455.
Since the standard valve 455 heads and Stage1 heads have the same casting numbers, you cannot tell a Stage1 from a standard 455 that way. The 2 letter engine code is stamped into the deck between the #5 and #7 spark plugs. The standard 455 is TR, and the Stage1 is TS.