There are two fans available up through 1974, early cars were equipped with a 15" fan and later ones with a 15 3/8" fan

(1973 240Z 1974 260Z Fuel System Modifications pdf, page 16)

Fan measurements, The 2 stock fans that came with my project 74 both measure 16" + or - a 1/16th. they are identical to each other except 1 is steel & 1 is plastic. Fan to rad meas, is 1 5/8". 71 Z is still around & has a 5 bladed flex fan on it. Fan diam. is 15". Alum. spacer is 2". Fan to rad meas. is 1". Individual blade meas, is 3 1/2" x 5 1/4". It is going on the 74 soon. We'll see what the future holds.Mark in Portland