Heres a picture of a 1946 truck radio:
http://46chevytruck.com/images/Accessories/DSC00238.JPGInstall it below the dash to the left of the steering wheel with an L-shaped bracket on each side of the radio up front and a slightly bent bracket from the stud on back of the radio to the end of the wishbone rod that extends thru the firewall.
Model 986146 is a Chevrolet Radio & is the correct radio for 1946. Another Chevrolet Radio used in the 46 was Model 985792.
The latter was a little less expensive.
Here is the best I've seen on the antenna location. The whole article is great information.
http://www.46chevytruck.com/