to sum up.. you need a different, Shorter, Bottom Bracket Spindle length to fit the "new" Crankset...

and, as someone that works on a wide range of old bikes, there are THREE general square/diamond crank styles.. i call them "Innies", "Flattes", and "Outties"

your old one shown is a "Innie" and they use the length Bottom bracket spindle that is still in the bike... around 123 to 127 mm length...
the new one looks like a "Flattie.. it will, most likely need a 118mm Spindle, but might need a 113mm spindle, depending on the bike's Frame

measure the Frame at the Bottom Bracket.. NOT the Bearing/spindle part, but the FRAME'S Tube that the 4 other tubes meet up at... it will be 68 or 73mm.

now... measure the width between the plates the rear wheel sits in between, and the axle clamps to... that is called the "Over Locknut Distance", or O.L.D. for short... it will be either 126, 130, or 135mm.
126mm and 130mm are road frames, and 135mm is an MTB frame.
(SOME really old MTB frames use 130mm O.L.D., but they are getting more rare by the day...)

report the measurements to this thread, and the bottom bracket spindle length you need can then be determined, ok?