Thanks to all for your replies.
When I went see the truck in person, I did find the tag on the driver's door jam. I was surprised to see that it too gave a range for the GVW. I expected a single number.
I decided to pass on buying this truck. It is in OK shape and in case it might be of interest to someone else here, here's the CL listing. (I have no relation to the seller or other interest in this sale).
http://boston.craigslist.org/sob/cto/933357900.html
