These special screws were in place until the ‘51 Model year when they went to rivets.
https://www.flickr.com/photos/advance-design_parts_co/9110621847/in/album-72157631868452754/
Here is a factory filmstrip shot from 1948 showing them.
https://www.flickr.com/photos/advance-design_parts_co/17057160050/in/album-72157651722976780/