The 1947-Mid-49’s should be like this, the 5-fuse panel, wiring harness is different for this purpose, this GMC truck I owned was a low mileage original. They should not have the two OEM, adding the other panel would give you a lot more fused circuits though. This is from the 1948 owners manual, you can see photo and instructions show the 5-fuse box only.
https://www.flickr.com/photos/advance-design_parts_co/50650482883/in/album-72157631872034068/
https://www.flickr.com/photos/advance-design_parts_co/29402434846/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/14200833813/in/album-72157631868452754/
Here you can see the page from the 1950 owners manual, 2-fuse block only.
https://www.flickr.com/photos/advance-design_parts_co/50650503243/in/album-72157631872034068/
The jar was a NOS Windshield Washer accessory (the jars are dated by year). I use orange Rainx fluid because it does not freeze.
https://www.flickr.com/photos/advance-design_parts_co/14039737010/in/album-72157631868452754/
The small black box is a period correct Chevrolet dealer service minder, it rewinds with a small key, they are fairly rare and usually don’t come with a key.
https://www.flickr.com/photos/advance-design_parts_co/8460965541/in/album-72157631867396207/
https://www.flickr.com/photos/advance-design_parts_co/8462063464/in/album-72157631867396207/