I like what you're doing with the motor box. Even with that, you've got quite a lot more weight to take out to get to 28lbs. I hope you make it! At this point, you might want to think of pull-pull rudder AND elevators as you might need to take the elevator servo weight out of the tail to balance something like the BME. Easier to design it now than after you're covered and painted.

Best of luck with your goal...........Mark