If you are building for gas you can also move the firewall back an inch or so if the model was designed for glow. Remember that a pound or two heavier engine up front can mean a handfull of ounces needed in the tail to balance the model. You set the C.O.G. dry so a fuel weight savings won't help you there.

Among ARFs the models with servos at the tail are just the cat's arse for gas choices.