Inspecting b box after failure, found straight cut prop gear missing 6 of the 57 teeth. All 19 crank gear teeth looked chewed on and spit out. The new c box has helical cut gears much heavier than the b box. Went with 2.62:1 to turn prop 2450 at engine at 6400. Adding clutch to reduce wear on crank at startup and idle. Pictures... Still working on project, then clean up, then pictures.