By the way, if you are looking for a way to verify if it is 753, a 753 bare frame w/o fork should weigh about 1600-1700 grams. A 531 frame w/o fork about 2000-2200 grams. This one should be on the low end of that range, because it is small.
Ideally you'd strip the frame (remove the fork, headset, bottle cage, downtube cable stops, and bottom bracket) but you can adjust for whatever is hard to remove.
Thanks, That's good advice. I will. It will be interesting to see.