Hi Mark, there is no factory mod for increasing the tail area, go to my album and you can see the dorsal fin and the vertical fin enlargement that I did. Adding a dorsal fin is very simple what I did was use 1/2" heavy wall alum tubing fabricated an attach bracket at the forward end and riveted it to the flat plate bracket for the radio ant aft of the turtle deck the aft end I used a 5" peice of square U channel that fit over the 1/2" alum tube cut the top part of the U channel out to slip over the vertical fin tubing and bolted it on the aft side of the tube (I do NOT drill into any of the structural tubing so as not to weaken them). I then just covered the fuselage as you normally would and you have a small dorsal fin. With the heavy walled tube it will take any loads execpt directly pushing on it for handling of the plane. As for the vertical fin area I used 0.020" thick alum made a forming jig to bend a nice rounded leading edge I added 2" of area to the fin, attached the top using a steel channel that fit over the top of the fin tubing used aircraft CherryMax rivets to attach the channel to the alum addition and did have to drill a hole in the tube at attach the channel there, at the bottom I just went with a screw thur the fin addition and the gap seal I had fabricated before just under the covered fin area ahead of the stablizer attach bracket. Like I posted before this improved the flt very nicely and it was one of the best mods I have made other than installing the HKS vs the 582.