I'd just like to point out for clarity that the clamp bolts normally serve only to hold the clamp top, which fixes the handlebar. Because of the design, there are few, if any shear forces. All tortional forces are instead transmitted directly from the riser to the steering shaft splines. In the modification with the spacers, the bolts appear to end up taking the entire turning force, too. If nothing else, the bolts now are weaker due to the unthreaded length, and are taking considerably more force, yet have not been increased in diameter. Conservative or not, I'm sure any engineer who reads this will start to squirm in his seat, and have nightmares about the possibilities.
-Scotty