Most Asian Aros, to my knowledge, grow to 2 feet. That said, a green might work for a 4x2x2. But try not to get anything as imposing as a G1 Red or Crossback, color isn't the only thing making them prized as they are also quite thick, so even at 2 feet, the overall size (In this case, height, not length) difference will already be VERY noticeable.
Just consolidate for a bigger tank, that 300L tank will only work as a growout and you'll have to make sure that within 4 months of purchase (Of the fish), you already can move it/them.
Good Luck on whatever you may do.