I am currently doing the same I have an old Trex 600 flybarless. I havent flown it yet but am running through the setup and thus far everything is working as it should. Check out youtube for traditional heli setup videos by Chris Olson. There has been numerous updates recently on the Copter-3.6 branch of ardupilot for traditional heli to make it easier to setup and make the default parameters better for new setups plus some updates to the throttle control including a 5 point throttle curve. I am using 3.6rc7 which I built from source.