I believe they are all 39. You see the correct guages for 39, the two piece windshield, no bead around the fender wheel opening (like 37-38), headlight hung on grill surround (went to fender in 41). It might be a 40, but 40's were kind of out there by themselves and I believe a 40 did have the rectangular instrument panel on the dash.
That's my guess.
Joe
