The 1.5 ton is a 1940 if it has the same dash as 41-46. The GMC cab is a 39 with the flat dash and round gauges. The 39-40 cab looks the same as 41-46 but the cowl is about 1 1/2 inch longer on the 41-46. Windshield will be the same.
I have a 39 GMC and I'm looking for that grill. Let's do some swapping. I sent you a PM.