You are correct the identification number is incorrect as it stands, but by modifying the PH to HP it becomes the correct information. (1950 Chevrolet * 1/2 ton * 116" Wheelbase * Los Angeles Ca.) Changing it may be a big problem for you though. You can get a new tag from a few vendors (the 1950 tag was screwed on, not riveted), but at this point you would be breaking the law. In 1950, these tags were not considered VIN (vehicle Identification Numbers) They were used as serial numbers that when checked would show the wheel base, Plant location and Gross Vehicle Weight. Many states actually used the engine number as the VIN. This also caused lot's of registration problems because of the engine changes throughout the years.
As the subject has already been broached, changed identification plates may mean it could be stolen. I am always concerned with overseas sales because of this.
At this point you are under the assumption that the truck is really a 1950 and that the title was processed incorrectly, but since it is also on the identification tag that's doubtful. Pictures of your firewall the drivers side cowl may help in determining if this truly is a 1950.
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THIS to cross check your numbers.