Lance asked ...
Assume for the question that both engines are running solid, does a bit of outward angle on the exhaust pipes help with any stablity issues?
One that comes to mind, is for example throttle changes if one engine is a second or two behind or ahead of the other one.
IMO highhorse has the hot tip: be thinking stability augmentation on the Z axis - that means a rate gyro on the rudder(s) to compensate for thrust vectoring.