Pictures will help but the fuel tank is a huge clue, it is a 1947-48 only item. The other thing you can look at is cab trim, the weatherstripping around the doors will be screwed on in sections. The headliner center rib will be welded in place with a screw on attachment bow to secure the headliner. The truck horns is an accessory for most years of AD trucks. Turn signals were another accessory available as a GM part or aftermarket (common). The Pontiac wheel was probably a PO preference because the steering wheels were one design only from 1947-53. If the springs are outboard of the frame you may have a 3600 instead of a 3100, pictures here would help narrow the series.
Here are some pictures to illustrate, wheel, dual horns, signals
http://www.flickr.com/photos/advance-design_parts_co/8130475256/in/set-72157631870734114
http://www.flickr.com/photos/advance-design_parts_co/8130448397/in/set-72157631870734114
http://www.flickr.com/photos/advance-design_parts_co/8129416019/in/set-72157631868452754




1950 Chevrolet 3/4-Ton 3600
More pictures on Flickr