Have just been looking through an old thread on the Studebaker tank and decided to start a new one to add my comments, as the thread had been dormant for over a year.
My observation is that the apparent difference between superstructure of the tank in the old photos and in cheffy's new one is not caused by any changes to the structure, but because of the shape of the structure at the front: the driver's cab does not appear to extend for the full width of the centre hull, but is offset towards the right, with a "bite" taken out of the superstructure at front left - hence Roger counted 19 rivets along the right side of the superstructure in cheffy's photo, but only 16 in the old pics showing the left side.
I also believe that the old pics cannot show a form of structure that was later modified to accept two pepper-pot turrets, as the old pics look to show a vehicle that has been put out to pasture (albeit perhaps recently) after the removal of turrets, but has yet to start rusting away in the manner of most vehicles pictured on Bovington heath in the '20s.