I understand your doubt in this bicycle, some items don't appear correct but the fact is it has it's original paint, original top tube and seat mast decal, original silkscreen chain guard, it's not a made up piece. There are no other bicycles Schwinn made Sting-ray or BMX with these features.
As for the front Hub it is just like the one on my 26" 1979 Spitfire 5, Heavy Duty small flange but installed on a 20" S-2 36 hole .105 gauge spokes.
What other Schwinn 20" would have had this Front Wheel?