probably a 240Z because I think the later models had bigger bumpers, but you never know cause it could just be modified.
240 was the early 70s, 260 I believe was only made in one year, and 280 was the late 70s.
easiest way to tell is by engine size. 240Z, 2.4L ; 260Z, 2.6L ; 280Z, 2.8L
I love those cars