Ford COE lower cab question?

I have been looking at a lot of Ford COE's lately. Trying to figure the differences between the years 39-47. ON bottom of cab there is what appears to be about a 2" raised area that goes around the back side of cab. On some of them that is the bottom of the cab but on others there is another 6" or so of material. Is this a year difference or are people cutting that bottom part off? Here is a pic of one to show what I am talking about.

 

The cabs are all the same, there are minor differences. The two inch rib is at the bottom of the cab. The extra 6" you see is the panel mounted to the cab to fill the space between the cab and running board.

Difference I know of are:
Some 38 inner doors are different.
there are two different stampings of inside windshield post covers
Running boards have two styles, visable bolt heads vs no bolt heads
Grills 38 (oval), 41 (stainless trim) and the 42-47 (waterfall)
Headlights - early adjusted by moving buckets, later sealed beams and adjustment screws

 

Thanks again KS, I really need to buy a cab so I can start planning this build. I have been trying to make plans before hand but there is just too much I don't know about the COE. lol

 

38-39 have round gauges as well as no park lights in the headlight stanchions.