Not a lot of ways to design a high wing cargo aircraft. the C-20 doesn’t have a T-tail, so it isn’t a direct copy of the C-17,
How much of it is alloy vs carbon? The C-17 has carbon wings.
The graphic on the Free Republic article page is probably an early design concept for the aircraft. The 12 photos at the Crienglish article definitely show a “T” tailed cargo aircraft that looks a lot like a C-17 without turbofan engines. (Sort of a C-17/Il-76 blend).