Weeds, most of the trucks that are being put back on the road have mutant parts from many sources (repops, other trucks, fabrications etc.) Although illegal (according to DMV) changing a VIN tag from one vehicle to another is common practice. Trucks are found abandon in fields, barns etc. and the owners have lost the paperwork, so the next best thing to do is find an old truck that is used for parts that has a title and switch them. Since the older trucks only have the VIN tag and no other markings it goes undetected by everyone except us!

Newer vehicles have multiple vin numbers on them in hidden places so that it can be detected if someone is illegally stealing a car and trying to disguise it.
Since you have a title and VIN plate that matches you will never be hassled by DMV. Since you have the body off of the frame you may want to stamp the numbers on the frame to protect your investment in the future. A good place to stamp it is by the steering box and a few places only you know. .........g