FWIW, Smokey Yunik was said to have swapped pistons out that were over 100 grams heavier or lighter without touching the balance in some of his race engines back i the day with no noticeable vibration.
I changed the pistons and cam in my 494" RB with the consultation and help of Dwayne Porter. He nailed it with my combination. Great man to work with and highly recommended even if its just to chat with him.
I changed from stock 360 pistons to KB107 flat top pistons without any balance like 16 years ago. Did unknowingly!! Engine seems to be strong and no vibrations after all these years. Did follow ring gap recommendation as per instructions.
