Look down into the engine compartment on the left side(driver's in USA) over the fender near the radiator mounts. Where the front crossmember is riveted to the frame rail you should see the VIN, a five-pointed star, a prefix, a dash, then the sequential numbers followed by another five-pointed star.
If it still has its original transmission, look on the bell of the trans case above the clutch inspection window. The number is stamped there. The number was originally****igned to the engine/trans unit, not the vehicle. When that engine/trans unit was bolted into a chassis, the number on the bell of the trans was copied onto the frame. The location varies because the number was stamped on the frame by hand. They literally had a guy with a set of number stamps and a big hammer who copied the number off the trans onto the frame. It's in 3 places on top of the left frame rail. The only one you can see with the body on the frame is the location others have already mentioned--it can be anywhere between front crossmember and firewall but usually right beside the steering box. The other locations are about where the back of the cab and front of the bed meet and on the arch over the rear axle. Sometimes the stamping is faint (all depends on how hard the guy with the hammer hit the number stamps), but it's there, may take some effort with a wire brush to find it.
The Jalopy Journal
