How do I tell if my 340 is internally balanced?

I bought it in a deal with my 68 Barracuda. I never heard it run, but he said it ran well. For a piece of mind, I am thinking about tearing all the way down and redoing everything.

That's a total waste of time and money. You don't rebuild the engines in your used daily drivers after you buy them do you?

I know how you feel... I used to think the same. Install it and run it... if it need to be repaired do it then. Otherwise drive the car and enjoy it...