Per
http://www.singahobby.com/osm06.html#30S the FS-30 is only 9 grams (1/3 ounce) heavier than the 26. The 40 is 76 grams (2.67 ounces) heavier than the 30. Keep in mind that many twins come out tail heavy because the weight of the engines are so close to the CG and the nose is typically short.
HTH,
John