I agree with Bill, H1 should work fine. I assume you are tilting the rotor fore and aft, and side to side, for directional control. Your throttle to vary the speed of the rotor to change thrust for vertical control will be on SERVO8 and just adjust the throttle curve (probably a linear 0-25-50-75-100 curve to start with). There will be no servo connected to SERVO3 - it won’t be used.
The autopilot will adjust the rotor speed by changing the collective on SERVO3 for altitude control, which is tied directly to the throttle on SERVO8 thru the throttle curve. Getting the throttle curve adjusted properly will be the “trick”, otherwise it should work fine.
I assume you are using a little motor on the tail for rudder, since changing the rotor speed with a transmission-driven tail will also change tail rotor speed and vary the yaw thrust. The Direct Drive Fixed-Pitch tail option in ArduPilot will work for that. DDFP changes the speed of the tail motor independent of the main rotor. I have flown DDFP on sizes up to 500 with good success. I tried it on 600 and it didn’t work due to a DDFP tail motor not having fast enough response for bigger helicopters.
If the helicopter is coaxial (two rotors turning in opposite directions) then you do not need a tail motor and yaw control is achieved by varying the differential speed, or collective pitch, of the two rotors. ArduPilot can only do this with coaxial helicopters by mechanical mixer that changes the collective pitch independently on the two rotors. It cannot handle a full fixed-pitch coaxial system that has two motors driving the rotors in opposite directions at independent speeds, as it has no mixer for that.