[J and M Machine]

Peter: the reciprocating parts Rods and pistons should be less than a 1/2 gram if you're able to do so. The engine will vibrate at 2 grams or more.
Ford balanced these engines and on average a stock crank is usually around 2-3 grams.

You'll find the biggest out of balance on the rods since they probably didn't come from the same engine and the next culprit is the flywheel and clutch assembly.

I would suggest balancing the clutch and flywheel as a unit and you may be amazed to see it from 10 -20 grams out of balance.