Jim,
I haven't built a Shark 402, but I have modified a Flite Streak and Skyray to two wheel configuration. I used the RSM aluminum gear like comes in their Ringmaster kit and it worked very well. As you were planning, I drilled 1/4" holes and plugged them with dowels. The gear then simply bolts on with 4-40 bolts and elastic lock nuts. I found this easier than installing a wire gear.
Steve