With no title nor a VIN plate, all you have is a pile of parts. You will need to buy another truck which has a title and a VIN plate. There are plenty of rust buckets for sale which are not worth restoring which you can buy, register with the DMV, and put your parts on.
I do not see any reasons why this approach would not be ethical. Although you will be taking the VIN plate off of one cab and putting it on another, it doesn't really matter since many of the titles were originally based on the engine serial number and not the VIN plate.
Just doing a paper shuffle and VIN plate swap obtained from someone who lacks scruples is not the way to go. What if the law cracks down on the guy who sold you the illicit title/VIN plate and comes down on you after you spent a fortune building your truck? By-by truck!
