piston questions

As stated, the factory balance is sub par at best. If you want an engine to live a long life, get the reciprocating components "balanced". This was drilled into me from a very young age by an old time engine builder who helped me into the hot rod industry. Don't get me wrong, I've built a few "grenade" motors from bits and pieces I had laying around, some of them survived for a few thousand miles, others never made a trip down my driveway. The cost of the initial balancing far out weighs starting from scratch when you bring the engine home in peach baskets. Ask me how I know.