Huben Ho to tell generations of the Huben K1 apart?

I am going to be buying my first Huben K1, it will be a secondhand gun, heard stories about the early versions and would like to know how to tell what generation I am looking at when I get one offered to me? On face value they all look the same, but there must be small things that will tell the generations apart. Don't want to end up with an early version.
 
Give Krazykool the serial #. Early versions had lw barrel. Good barrel but bad choice for this gun. Later models have Chinese barrel. Much better match and shoots pellets very well. Picky for slugs. If you need more info just ask Kelly at Krazykool. He’s very helpful, he sells repairs and customizes gk1 and k1 givens. Also sells appropriate ammo to match
 
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