Model 12-16ga How to determine if field grade or trap

Just wondering if anybody know how to determine if my model 12-16ga is a field grade, trap or other. Manufactured in 1939, #778---.

theres no exact way unless you'd contact winchester for records of which grade it was when made ,,the books say the trap version had a checkered slide extension,and a 30"round barrel with a solid or vented rib,,with fancy walnut straight or pistol grip stock,,it would also have a solid recoil pad,,this is the description straight from the books..
bigcurt