So in other words, if you are right, then the dirt bike's headset components are INDEED stronger than Toyota knuckle bearings. As crazy as it sounds, you'd better believe it! Perhaps that is why Yamaha's are so expensive! Gotta love Japanese quality!! 
No.
I see no way that a dirtbike steering head bearing would be stronger than a bearing designed to carry steering load on a 4800-pound truck. I do see a shear strength increase over stock on behalf of the pin, but this isn't really the issue at hand. Although I do know that you guys have had some high-steer arm issues related to the pin.
what I am getting at, is that the load the bearing is designed to see is lower than what it will see in your application, and it is a light duty bearing.
