well unless you had it blueprinted  and everything put in little baggies,   you changed the weight of the rods, pistons etc

and ive NEVER  bought a set of pistons  off the shelf  that were the same exact weight

get real 

I mean like from cast to forged. I have never balanced any of the stock rebuilds I have done and have done plenty and never have had a problem. The only engines I have balanced were ones that I went to forged pistons with different pins and the rods were changed or polished. Oh and as far as putting everything in little baggies, is there any other way.