I have the Grand Sport stripped down to the bare frame. With the fork and headset (no BB) it weighs 7 lbs. 2 oz. I measured my '72 SuperCourse, which is also a 23.5" frame, to be 7 lbs. 13 oz. That is a difference you can feel when you lift them.
Based on the SN, the GS is a 1973 model. The frame geometry between these two frames is the same, except the GS wheelbase is longer at 41.5" vs. 41" for the SC. The GS top tube is 1/4" longer and the fork has 2.5" rake instead of 2.25" on the SC. The GS head tube is 1/4" longer also. Overall, this GS is a stretched version of the SC with a lighter tubeset.