Well a few things that I note in the initial design:
A flat plate on the side isn't going to prevent flex or twist. The bosses it's bolted to will just snap off (they snap from simple road debris impact sometimes).
You will need get the plate bolted at the 5mt's strongest points, the bell housing bolts and the transfer case attachment points to make it effectively stop the flex and twist in the main case.
The front tube piece has no vertical reinforcement so it will twist with the case and probably break the case at the front diff where it is bolted to.
I think if you can combine your two pieces then we'll be headed down the right road.
If you are going to try and test the designs you will need to apply about 600 ft/lbs of shock load to the input shaft while keeping the front diff and rear output shaft stopped.
A slowly applied torque load will not be able to create the kind of load see even under normal driving and that's alot less than a launch.
-Dylan @ DS1
(your average pessimist