Adverse yaw is seldom an issue with powered models and the usually lower aspect ratios. What happened here sounds much more like a very agravated stall and snap roll.

DR, don't jump to conclusions. The forward CG may have been a contributor to the overall problem but it may not have been the only issue.

How did the other Agwagon fly? Did you ever check to be sure the wings were totally flat from center to tip? Or better yet, had a little bit of washout? That's where the tips have a couple of degrees of trailing edge up angle compared to the center section. Makes for less tendency to tip stall. Is there enough of the wing left to check for this?