[CSHADES]

The rubber around the rear window is also a sign of what year it is. If the window bolts in it is a 1941 if it grabs the pinch weld with no bolts it is a 1946. I don't know which way it goes if it is a 1942. The vin tag is on the right side of the cowl. It may not be the actual number that is on the title because of the use of engine numbers and not actual vin number. The idea of installing a 350 now and then reinstalling the original engine later is not really a feasible thought. It takes some engineering to install a v8 in these trucks especially with the original steering and suspension. Also putting a v8 in will over power the brakes and steering. These trucks were designed to carry weight at slow speeds (45 mph and under)
My suggestion is if you can find someone that has one of these in original running condition is to ride with or drive if possible and then you can make an educated decision on what you want out of the truck.
I own and drive a 1940 1/2 ton almost everyday in the summer(modern drivetrain) and I have a 1946 1/2 ton here at the shop that is original that I wouldn't drive across town any day. But it is all up to the person that owns it and has to live with it.