Some Eastern roads, made the move to wider doors with new equipment (or
rebuilds) after the war. Wider doors allowed the use of mechanical loading
equipment (folk lifts etc) and so were popular with railroads with a large
manufacturing base.
I presume the move from 7ft to 8ft was to further improve mechanical access.

The Pennsy introduced a 7ft door with class X37 (ok pre-war, whats this,
Altoona making a progressive step in freight car design ?!?!?! ), and
continued to use this size for its post war rebuilding programs. X26(USRA
SS) and X29 rebuilds received new bodies with 7ft doors. X43 / X43a / X43b
also had 7ft doors however X43c featured a 8ft door. The next batch of X29
rebuilds, X29d received 8ft doors.

Reading's post war boxcars all received 8ft doors.

CNJ had several groups of 7ft door cars (lettered CRP).

SP had several large classes of 7ft door cars, I do not remember the class.

Ian Clasper