Do some reading in the repair manual. Start here and read a page or two forward or backward. I think it'll explain what you need.
Its suppose to cover 51 so it should show the wind vent to.

http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0110.htm


1937 Chevy Pickup
In the Gallery
1952 Chevy Panel
In the Gallery
More photos
1950 Chevy Coupe
Pictures!

I'd rather walk and carry a Chevy hub cap than ride in a Ferd.
I can explain it to you, but I can't understand it for you smile