Hey Andy - Sorry it's taken me a bit to get in here and offer some response to your question. I'll start with some original Chevy resource info specific to your 1947.2.
Below are a couple of screenshots (first 3 below) of your inside windshield trim center cap top and bottom taken from this original
1947 Advance Design Chevrolet Trucks film strip courtesy of Brad Allen.
The first screenshot appears like there is no screw holding down the lower center trim cap.
But the next two show the same part with a screw to retain it in place both bottom and top.
The next 2 screenshots come from the original
1947 - The Cab That Breathes film strip, also courtesy of Brad Allen.
Each of those show both lower and upper center trim pieces retained with screws that look the same as the ones for the main trim pieces.
The last tidbit I have to offer involves a closer look at your first "no holes" picture. I zoomed in and snapped a screenshot (last pic below) that appears to look like there is a possible screw hole "dimple" for the lower trim cap that maybe never got drilled when built, which would have prevented proper install of that trim cap. I did not find a similar "dimple" in your upper spot picture, but pretty sure you should have no problem drilling one to secure the upper center trim piece.
Let us know how things turn out.
