JohnRR,
I did explore the tapered roller bearing idea. This would make a special bearing retainer necessary then. We were striving to use all factory type hardware. That would minimize the cost of retrofitting the aluminum cases to your application. The factory 308 bearing is a high load bearing so I don't see the retrofit to be worth it. We have tested them and I feel that they should hold up fine to whatever you can throw at them within reason.