The left-side cowl (driver's side) ventilator was removed in 1951. The top cowl ventilator and the right-side (passenger's side) ventilator was there all Advance-Design years.
In late 1949, two cab-interior changes were the cab door-opening windlace track and the headliner bow was no longer screwed in.
A subtle change that I think people bring up during this type of discussion is a slight change in the appearance of the firewall), but I do not recall which year.
