[barabar]

I have built a few motors and even had webbings break. Keeping the complete rotating assembly balanced (fly wheel,clutch and pressure plate too) is very important. Girdles are no more then frosting on a cake. 4 bolt or cross bolt the mains, 6800 rpm and above seems to be the point to do this. Also depends on what block you are using.
Bottom line---Balance and 4 bolt mains.