I have the Decathlon with an OS .91FX in it.....I also have a Slimline "pitts" style muffler on it which really makes the engine sound like a four stroke! I put Futaba's 3151 low cost digital servos in it too with a 1000 Mah Ni-Cad....all is fine, but of course there is some trimming of the cowl to be done, but not much.....if you put the "Pitts" style muffler on it....Good luck with your decathlon
Blair