While the engines where in the test stand being run tested,we used to pin the harmonic balancers with wt's.I did that as apart of the test cycle when I worked at a Chevy engine plant.The thing was the factory tolerances where pretty wide and guys used to re-balance their engines to get a better balance job.
You said the engine is pretty rusty..060 is about as much I would want to go under.(actually I am used to cranks measuring either .010/.010 or .020/.020.The thought being a concern for it being cut beyond the hardness of the crank)If you could post some pictures of the crank,it would give us a better idea of the condition of your crank so we could best advise you from there.