With the type of Y harness I used i didnt have to use any servo extensions. the only one was for the connection of the y harness to the reciever. The airplane came with its own spinner and I would go for the 12.25X3.75 APC for the prop on an AX. I know that sounds like a crazy size but give it a try and you will be amazed. I use a 13X6 on the Saito.