Found a guy that claims to have "many" '30s-'40s trucks, 1/2 ton on up, both complete and in pieces (including COEs). Also have a local yard that specializes in antique autos and parts. Both indicate that parts may be scattered about and un-identified.
How can I ID different parts on the spot?

What I think I know...
1) In '36 the headlights moved from fenders to grille and it was last year of "swoopy" dash.

2) 1939 Major re-design of nose and fenders. Lights went back to fenders but stayed close to grille. Fenders got 3(?) grooves at trailing edge.

3) 1941(?) Lights moved farther out on fenders. Now centered on the character line.

4) '48+ I could recognize enough but I'm not interested in those...yet.