I have now got this working. this is the pixhawk build
Parameters should be set so Q_FRAME_CLASS = 10 and Q_TILT_TYPE = 3. Flys OK, pitch in the hover is very tricky to tune and it defiantly cant go backwards.
updated PR is here Plane: add bi-copter tilt rotors quadplanes by IamPete1 · Pull Request #10793 · ArduPilot/ardupilot · GitHub
I suggest you get your plane built and flying in forward flight, then we can go over the setup for the hover.