These are aftermarket wheels with 20" tires and likely won't have the same limitations. Unfortunately the GVWR and the axle ratings are part of the federally mandated sticker which can't be changed. If you run into a sufficiently motivated cop he will write a ticket for over weight.
BTW the build sheet also shows this:
Company Car Tracking
Marketing / Public Relations Vehicle
Sold Vehicle
Special Scheduling Condition VII
Reliability Test Vehicle
I would pass on the vehicle because it likely has been beat on by a number of people.