And there are significant technology differences. The new upgrade will be the B-52J or K.
Proper aircraft maintenance cycles are intense, so it would surprise me if any of airframes we use now have 1952 original parts. Aircraft are subject to lots of vibration and the aluminum in B-52s will eventually stress-crack because of it. (It wouldn’t surprise me if composites were added in many places instead of aluminum replacements, but that is just speculation.)
Also during those maintenance cycles, it’s much easier to do systems upgrades since the aircraft is basically torn down to its frame anyway.
It’s the same design to what we had in 1952, but they ain’t the same aircraft, philosophically speaking.