The kit grill is not a 40 grill from all the picture I have found of a 1940 Willy's . It is a grill that race car drivers used ,It has no center bar .
The wings as you call them should not be peaked as they are in the kit. They should be more like the Revell coupe kit.
They had a flat head four just like the jeep's from the war. That should be close enough .
Just call your truck a 1941 and use the kit grill. Put the Wipers on the bottom.