Hi Nick

I think the answer is already here amongst what’s already been posted, but could benefit from being put together in one place.

To start… I think we need to clarify the origin of your (Nick’s) floor pan.
A couple of things tell me it is not a reproduction, but an actual original old pan.
The screw holes are the large taper formed holes for the flat counter sunk slotted screw heads originally used to screw down the pan.
And, the metal around them is “pulled” and worn from use (in fact, many of holes in original pans I’ve seen are worn to the point that the original screws pull through them).
One of the holes is even torn open.
And, why would someone go to the expense of reproducing the “hump” in the middle when it isn’t needed?

As Rusty points out, gleaning information from Chevrolet parts books can be difficult due to elimination of listings for parts no longer furnished, or substitution of “will work” parts.

Nevertheless… starting with 1940, and excluding COE’s, all of the floor pan variations can be described and divided up on the basis of 3 things:

Years:
1940 is a stand alone year. 1941 through ’46 can be grouped together.

Truck size:
½ tons stand alone, all others ¾ ton and up are different.
The difference lies in the location of the master cylinder fill hole.

Transmission:
3-speeds use different pans than 4-speeds.
The difference here lies in the shape of the hole for the gear shift tower.

So:
There were 4 pans for 1940:
a 3-speed ½ ton, a 4-speed ½ ton, a 3-speed ¾ ton, and a 4-speed ¾ ton, and 1-1/2 ton.
For 1941 to 46 there was:
a 3-speed ½ ton, a 4-speed ½ ton, a 3-speed ¾ ton, and a 4-speed ¾ ton and up.

Then there is the “war production” in inventory at the end of the war as pointed out by 37Blue.
I also have heard of and seen the remnants of war production making their way into 1945 and ’46 trucks, including the leather gas filler grommet on my own truck. (Yes there were 1945 model year civilian production trucks!)
I think the “hump” is exactly that.

So…
From that, based on the master cylinder filler location, the round tower hole, and the “hump”, I think your floor pan is an original floor pan from a 1945 or early 1946 3-speed ½ ton truck.
But I could easily be wrong. 🙂