Mark,
The yellow bar isn't optional. Otherwise you have designed a fulcrum if you have a hard landing. Most of the mounts being designed now go directly to the engine/gearbox interface. The plate will work too, but try to connect to the load as far forward as possible. Of course don't forget the prop mass as even a wood prop or composite are going to weigh a few pounds! 15 or more isn't out of possibility and that would be at least a foot in front of the end of the plate mount.
Bill Jepson