I had my 273 rebalanced when I had the machine work done. I think it was either 50 or 75 and will be well worth it. For me the main reason to balance is longevity of the engine. An out of balance lower end will wear out bearings faster and cause rod bearing failure sooner.

Even using stock .030 over 10.5:1 pistons, I had to change out one rod, and rebalanced not only for that rod, but because the pistons were +-.05 grams. Rick took a fair amount off the back of the #1 rod.