Bill,
You must have me confused with other person. I also do not use out thrust and center my engines. I did have to add down thrust on the Twin Ugly Stick, after, as Bill said, I flew it and found what was needed.
Whole project sounds cool. If you plan on aerobatics with this plane, increase the rudder size, put the engines on separate channels, and mix the engines to the rudders....above 50% throttle setting for safety. You cannot imaging how easy the knife edge is with differential thrust. Getting into and out of a flat spin, is merely reversing the rudders..ect ect!!!
OK, so I have lost it!!!!!
PS Also mix the ailerons to the elevator. More lift for manuvers and reduced unexpected snap rolls.