Jay,
I use one Hitec 615MG servo for each elevator half. These servos, as well as the rudder servo, retracts and kill switch servo are all located on a servo tray that I designed and is located directly under the belly pan opening. The elevators use carbon fiber rods and 4-40 harware.
I took one look at the flap design and asked myself one question . . . why? It is not only easier, but far more reliable to simply put one flap servo in each wing panel. I highly recommend doing that over the stock plan.
I love my Hellcat and you will too.
Give you guys a short war story on just how stable this model is (and by the way mine weighs in around 32 lbs). The last flight I had, I made my final approach all the way until touch down without my flaps deployed. I thought I hit the flap switch, but I did not get it all the way down. The Hellcat slowed to a crawl before she just started to wobble a bit. Then I realized my mistake, powered up and went around again. This time, the flaps were down and she slicked right in.
I included a few shots of the servo set up. Also one of the Cat stored away awaiting its next sortie.
Good luck and have fun.