Could it be real 18th century counterfeiter's work

Hello,
I’m an proud owner of 1783 year coin, Reverse is “Grosz - Stanisław August Poniatowski”

but Obverse is “1/24 Thaler - Friedrich II” and sides are cut off to meet Thaler size, looks like 18th century counterfeiters have made modifications to Grosz to give it out as a Thaler, over time it lost coloring modifications.
Would you be so kind to give some light to following questions:

• How rare or common is such a modification
  
• Are there any interest from numismatists for such coin
  
• What could be its current value
  

Indeed strange coin.
I know there are collectors for forged coins.
Value? No idea.
Do you see something strange on the rim (line?)
It could be a cast coin with the image of a gross/thaler