I think all 753 serial start with SB or the initials of the rider in case it were a bike for the team. My 753 looked not alike yours in detailing, for example the crown, the lugs I not recognize as being of a 753 frame. My frame had (in case of my frame drilled) Campa drop outs instead of ...Gipiemme. Maybe I am all wrong and you got a true gem there, but I would recommend taking a look here >>>
Maybe you can derive model from frame and specs.
Of course when you disassemble it you will feel it when lifting the frame.
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