To go along with what Ghengis said.
The shells will swap with no issue, I've done it several times.
One thing to watch for, the first time I did this I noticed the headlight wasn't very bright.
On the old chassis the the LED was up and right behind the glazing.
With the DCC ready chassis they extended the light tube so that it extends and bends down, right in front of the surface mount LED which sits back on the drop-in chip.
If you can find these new glazing they are also interchangeable into the old shells.