Question about balancing rotating assembly

When you are a normal dumb-***, you sit around arguing about which spark plug or motor oil will turn your car into a Top Fuel dragster. When you start to feel smarter, you start espousing the merit of equal length, tuned exhaust systems and camshaft profiles. Then, when you are an expert you are confident enough to start the balancing and rod/stroke ratio discussions.

So anyway, just for the sake of mentioning it....I owned a '70 340 Swinger that I bought from the original owner in 1986. It had about 113K miles on it and ran great. There is absolutely zero chance anyone had ever been into the engine. When I did take it apart finally, I found one journal had 318 rods instead of the 340 rods like the rest of the engine. Significantly lighter. I did a lot of reading up in Hot Rod and Car Craft and determined the engine had to be shaking violently, even though it showed no signs of it and ran as smooth as butter.